diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index 22b6636b5..ab69effb3 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,4 +1,5 @@
 September 6, 2009  (Changes by Graf Zahl)
+- changed line_t's sidenum into sidedef pointers.
 - changed side_t's linenum into a linedef pointer.
 - Added PinkSilver's SetActorVelocity code submission (with optimizations.)
 
diff --git a/src/d_net.cpp b/src/d_net.cpp
index 8a1d10e4c..80c8de130 100644
--- a/src/d_net.cpp
+++ b/src/d_net.cpp
@@ -2188,7 +2188,7 @@ void Net_DoCommand (int type, BYTE **stream, int player)
 				{
 					DImpactDecal::StaticCreate (s,
 						trace.X, trace.Y, trace.Z,
-						sides + trace.Line->sidenum[trace.Side], NULL);
+						trace.Line->sidedef[trace.Side], NULL);
 				}
 			}
 		}
diff --git a/src/g_shared/a_decals.cpp b/src/g_shared/a_decals.cpp
index 06f42a302..a4de80938 100644
--- a/src/g_shared/a_decals.cpp
+++ b/src/g_shared/a_decals.cpp
@@ -175,10 +175,9 @@ void DBaseDecal::SerializeChain (FArchive &arc, DBaseDecal **first)
 void DBaseDecal::GetXY (side_t *wall, fixed_t &ox, fixed_t &oy) const
 {
 	line_t *line = wall->linedef;
-	DWORD wallnum = DWORD(wall - sides);
 	vertex_t *v1, *v2;
 
-	if (line->sidenum[0] == wallnum)
+	if (line->sidedef[0] == wall)
 	{
 		v1 = line->v1;
 		v2 = line->v2;
@@ -235,7 +234,7 @@ FTextureID DBaseDecal::StickToWall (side_t *wall, fixed_t x, fixed_t y, F3DFloor
 	FTextureID tex;
 
 	line = wall->linedef;
-	if (line->sidenum[0] == DWORD(wall - sides))
+	if (line->sidedef[0] == wall)
 	{
 		front = line->frontsector;
 		back = line->backsector;
@@ -307,7 +306,7 @@ fixed_t DBaseDecal::GetRealZ (const side_t *wall) const
 	const line_t *line = wall->linedef;
 	const sector_t *front, *back;
 
-	if (line->sidenum[0] == DWORD(wall - sides))
+	if (line->sidedef[0] == wall)
 	{
 		front = line->frontsector;
 		back = line->backsector;
@@ -359,10 +358,9 @@ fixed_t DBaseDecal::GetRealZ (const side_t *wall) const
 void DBaseDecal::CalcFracPos (side_t *wall, fixed_t x, fixed_t y)
 {
 	line_t *line = line = wall->linedef;
-	DWORD wallnum = DWORD(wall - sides);
 	vertex_t *v1, *v2;
 
-	if (line->sidenum[0] == wallnum)
+	if (line->sidedef[0] == wall)
 	{
 		v1 = line->v1;
 		v2 = line->v2;
@@ -393,7 +391,7 @@ void DBaseDecal::CalcFracPos (side_t *wall, fixed_t x, fixed_t y)
 static void GetWallStuff (side_t *wall, vertex_t *&v1, fixed_t &ldx, fixed_t &ldy)
 {
 	line_t *line = line = wall->linedef;
-	if (line->sidenum[0] == DWORD(wall - sides))
+	if (line->sidedef[0] == wall)
 	{
 		v1 = line->v1;
 		ldx = line->dx;
@@ -415,18 +413,17 @@ static fixed_t Length (fixed_t dx, fixed_t dy)
 static side_t *NextWall (const side_t *wall)
 {
 	line_t *line = line = wall->linedef;;
-	DWORD wallnum = DWORD(wall - sides);
 
-	if (line->sidenum[0] == wallnum)
+	if (line->sidedef[0] == wall)
 	{
-		if (line->sidenum[1] != NO_SIDE)
+		if (line->sidedef[1] != NULL)
 		{
-			return sides + line->sidenum[1];
+			return line->sidedef[1];
 		}
 	}
-	else if (line->sidenum[1] == wallnum)
+	else if (line->sidedef[1] == wall)
 	{
-		return sides + line->sidenum[0];
+		return line->sidedef[0];
 	}
 	return NULL;
 }
@@ -775,7 +772,7 @@ void ADecal::BeginPlay ()
 			if (trace.HitType == TRACE_HitWall)
 			{
 				decal = new DBaseDecal (this);
-				wall = sides + trace.Line->sidenum[trace.Side];
+				wall = trace.Line->sidedef[trace.Side];
 				decal->StickToWall (wall, trace.X, trace.Y, trace.ffloor);
 				tpl->ApplyToDecal (decal, wall);
 				// Spread decal to nearby walls if it does not all fit on this one
diff --git a/src/g_strife/a_strifeitems.cpp b/src/g_strife/a_strifeitems.cpp
index 15bb4fbd2..06674a1ae 100644
--- a/src/g_strife/a_strifeitems.cpp
+++ b/src/g_strife/a_strifeitems.cpp
@@ -32,8 +32,8 @@ DEFINE_ACTION_FUNCTION(AActor, A_RemoveForceField)
 		{
 			line->flags &= ~(ML_BLOCKING|ML_BLOCKEVERYTHING);
 			line->special = 0;
-			sides[line->sidenum[0]].SetTexture(side_t::mid, FNullTextureID());
-			sides[line->sidenum[1]].SetTexture(side_t::mid, FNullTextureID());
+			line->sidedef[0]->SetTexture(side_t::mid, FNullTextureID());
+			line->sidedef[1]->SetTexture(side_t::mid, FNullTextureID());
 		}
 	}
 }
diff --git a/src/nodebuild_utility.cpp b/src/nodebuild_utility.cpp
index 112defcda..3e50368cf 100644
--- a/src/nodebuild_utility.cpp
+++ b/src/nodebuild_utility.cpp
@@ -120,7 +120,7 @@ void FNodeBuilder::MakeSegsFromSides ()
 
 	for (i = 0; i < Level.NumLines; ++i)
 	{
-		if (Level.Lines[i].sidenum[0] != NO_SIDE)
+		if (Level.Lines[i].sidedef[0] != NULL)
 		{
 			CreateSeg (i, 0);
 		}
@@ -129,10 +129,10 @@ void FNodeBuilder::MakeSegsFromSides ()
 			Printf ("Linedef %d does not have a front side.\n", i);
 		}
 
-		if (Level.Lines[i].sidenum[1] != NO_SIDE)
+		if (Level.Lines[i].sidedef[1] != NULL)
 		{
 			j = CreateSeg (i, 1);
-			if (Level.Lines[i].sidenum[0] != NO_SIDE)
+			if (Level.Lines[i].sidedef[0] != NULL)
 			{
 				Segs[j-1].partner = j;
 				Segs[j].partner = j-1;
@@ -169,7 +169,8 @@ int FNodeBuilder::CreateSeg (int linenum, int sidenum)
 		seg.v1 = (int)(size_t)Level.Lines[linenum].v2;
 	}
 	seg.linedef = linenum;
-	seg.sidedef = Level.Lines[linenum].sidenum[sidenum];
+	side_t *sd = Level.Lines[linenum].sidedef[sidenum];
+	seg.sidedef = sd != NULL? int(sd - sides) : int(NO_SIDE);
 	seg.nextforvert = Vertices[seg.v1].segs;
 	seg.nextforvert2 = Vertices[seg.v2].segs2;
 
diff --git a/src/p_3dmidtex.cpp b/src/p_3dmidtex.cpp
index e408891bf..94df21d8c 100644
--- a/src/p_3dmidtex.cpp
+++ b/src/p_3dmidtex.cpp
@@ -56,8 +56,8 @@ bool P_Scroll3dMidtex(sector_t *sector, int crush, fixed_t move, bool ceiling)
 	{
 		line_t *l = scrollplane.AttachedLines[i];
 
-		sides[l->sidenum[0]].AddTextureYOffset(side_t::mid, move);
-		sides[l->sidenum[1]].AddTextureYOffset(side_t::mid, move);
+		l->sidedef[0]->AddTextureYOffset(side_t::mid, move);
+		l->sidedef[1]->AddTextureYOffset(side_t::mid, move);
 	}
 
 	// Second step: Check all sectors whether the move is ok.
@@ -87,8 +87,8 @@ void P_Start3dMidtexInterpolations(TArray<DInterpolation *> &list, sector_t *sec
 	{
 		line_t *l = scrollplane.AttachedLines[i];
 
-		list.Push(sides[l->sidenum[0]].SetInterpolation(side_t::mid));
-		list.Push(sides[l->sidenum[1]].SetInterpolation(side_t::mid));
+		list.Push(l->sidedef[0]->SetInterpolation(side_t::mid));
+		list.Push(l->sidedef[1]->SetInterpolation(side_t::mid));
 	}
 }
 
@@ -215,11 +215,10 @@ void P_Attach3dMidtexLinesToSector(sector_t *sector, int lineid, int tag, bool c
 //============================================================================
 bool P_GetMidTexturePosition(const line_t *line, int sideno, fixed_t *ptextop, fixed_t *ptexbot)
 {
-	side_t *side = &sides[line->sidenum[sideno]];
-	FTextureID texnum = side->GetTexture(side_t::mid);
-
-	if (line->sidenum[0]==NO_SIDE || line->sidenum[1]==NO_SIDE || !texnum.isValid()) return false;
+	if (line->sidedef[0]==NULL || line->sidedef[1]==NULL) return false;
 	
+	side_t *side = line->sidedef[sideno];
+	FTextureID texnum = side->GetTexture(side_t::mid);
 	FTexture * tex= TexMan(texnum);
 	if (!tex) return false;
 
diff --git a/src/p_acs.cpp b/src/p_acs.cpp
index 9cb2afe92..2ffd2663f 100644
--- a/src/p_acs.cpp
+++ b/src/p_acs.cpp
@@ -2163,9 +2163,9 @@ void DLevelScript::SetLineTexture (int lineid, int side, int position, int name)
 	{
 		side_t *sidedef;
 
-		if (lines[linenum].sidenum[side] == NO_SIDE)
+		sidedef = lines[linenum].sidedef[side];
+		if (sidedef == NULL)
 			continue;
-		sidedef = sides + lines[linenum].sidenum[side];
 
 		switch (position)
 		{
@@ -2883,15 +2883,15 @@ int DLevelScript::SideFromID(int id, int side)
 	if (id == 0)
 	{
 		if (activationline == NULL) return -1;
-		if (activationline->sidenum[side] == NO_SIDE) return -1;
-		return sides[activationline->sidenum[side]].Index;
+		if (activationline->sidedef[side] == NULL) return -1;
+		return activationline->sidedef[side]->Index;
 	}
 	else
 	{
 		int line = P_FindLineFromID(id, -1);
 		if (line == -1) return -1;
-		if (lines[line].sidenum[side] == NO_SIDE) return -1;
-		return sides[lines[line].sidenum[side]].Index;
+		if (lines[line].sidedef[side] == NULL) return -1;
+		return lines[line].sidedef[side]->Index;
 	}
 }
 
@@ -5416,7 +5416,7 @@ int DLevelScript::RunScript ()
 		case PCD_GETLINEROWOFFSET:
 			if (activationline)
 			{
-				PushToStack (sides[activationline->sidenum[0]].GetTextureYOffset(side_t::mid) >> FRACBITS);
+				PushToStack (activationline->sidedef[0]->GetTextureYOffset(side_t::mid) >> FRACBITS);
 			}
 			else
 			{
diff --git a/src/p_buildmap.cpp b/src/p_buildmap.cpp
index ee1d44264..4e44e1c26 100644
--- a/src/p_buildmap.cpp
+++ b/src/p_buildmap.cpp
@@ -539,8 +539,8 @@ static void LoadWalls (walltype *walls, int numwalls, sectortype *bsec)
 		}
 
 		j = int(intptr_t(sides[i].linedef));
-		lines[j].sidenum[0] = i;
-		lines[j].sidenum[1] = walls[i].nextwall;
+		lines[j].sidedef[0] = (side_t*)(intptr_t)i;
+		lines[j].sidedef[1] = (side_t*)(intptr_t)walls[i].nextwall;
 		lines[j].v1 = FindVertex (walls[i].x, walls[i].y);
 		lines[j].v2 = FindVertex (walls[walls[i].point2].x, walls[walls[i].point2].y);
 		lines[j].frontsector = sides[i].sector;
@@ -621,19 +621,25 @@ static void LoadWalls (walltype *walls, int numwalls, sectortype *bsec)
 			CalcPlane (slope, sectors[i].ceilingplane);
 		}
 		int linenum = int(intptr_t(sides[bsec->wallptr].linedef));
+		int sidenum = int(intptr_t(lines[linenum].sidedef[1]));
 		if (bsec->floorstat & 64)
 		{ // floor is aligned to first wall
-			R_AlignFlat (linenum, lines[linenum].sidenum[1] == (DWORD)bsec->wallptr, 0);
+			R_AlignFlat (linenum, sidenum == (DWORD)bsec->wallptr, 0);
 		}
 		if (bsec->ceilingstat & 64)
 		{ // ceiling is aligned to first wall
-			R_AlignFlat (linenum, lines[linenum].sidenum[1] == (DWORD)bsec->wallptr, 0);
+			R_AlignFlat (linenum, sidenum == (DWORD)bsec->wallptr, 0);
 		}
 	}
 	for(i = 0; i < numsides; i++)
 	{
 		sides[i].linedef = &lines[intptr_t(sides[i].linedef)];
 	}
+	for(i = 0; i < numlines; i++)
+	{
+		lines[i].sidedef[0] = &sides[intptr_t(lines[i].sidedef[0])];
+		lines[i].sidedef[1] = &sides[intptr_t(lines[i].sidedef[1])];
+	}
 }
 
 //==========================================================================
diff --git a/src/p_doors.cpp b/src/p_doors.cpp
index 1166d47f0..090065fb4 100644
--- a/src/p_doors.cpp
+++ b/src/p_doors.cpp
@@ -264,7 +264,7 @@ void DDoor::DoorSound (bool raise) const
 				if (line->backsector == NULL)
 					continue;
 
-				FTexture *tex = TexMan[sides[line->sidenum[0]].GetTexture(side_t::top)];
+				FTexture *tex = TexMan[line->sidedef[0]->GetTexture(side_t::top)];
 				texname = tex? tex->Name : NULL;
 				if (texname != NULL && texname[0] == 'D' && texname[1] == 'O' && texname[2] == 'R')
 				{
@@ -383,14 +383,14 @@ bool EV_DoDoor (DDoor::EVlDoor type, line_t *line, AActor *thing,
 			return false;
 
 		// if the wrong side of door is pushed, give oof sound
-		if (line->sidenum[1] == NO_SIDE)			// killough
+		if (line->sidedef[1] == NULL)			// killough
 		{
 			S_Sound (thing, CHAN_VOICE, "*usefail", 1, ATTN_NORM);
 			return false;
 		}
 
 		// get the sector on the second side of activating linedef
-		sec = sides[line->sidenum[1]].sector;
+		sec = line->sidedef[1]->sector;
 		secnum = int(sec-sectors);
 
 		// if door already has a thinker, use it
@@ -596,10 +596,10 @@ void DAnimatedDoor::Tick ()
 				// IF DOOR NEEDS TO ANIMATE TO NEXT FRAME...
 				m_Timer = m_Speed;
 
-				sides[m_Line1->sidenum[0]].SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
-				sides[m_Line1->sidenum[1]].SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
-				sides[m_Line2->sidenum[0]].SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
-				sides[m_Line2->sidenum[1]].SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
+				m_Line1->sidedef[0]->SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
+				m_Line1->sidedef[1]->SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
+				m_Line2->sidedef[0]->SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
+				m_Line2->sidedef[1]->SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
 			}
 		}
 		break;
@@ -631,10 +631,10 @@ void DAnimatedDoor::Tick ()
 				// IF DOOR NEEDS TO ANIMATE TO NEXT FRAME...
 				m_Timer = m_Speed;
 
-				sides[m_Line1->sidenum[0]].SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
-				sides[m_Line1->sidenum[1]].SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
-				sides[m_Line2->sidenum[0]].SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
-				sides[m_Line2->sidenum[1]].SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
+				m_Line1->sidedef[0]->SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
+				m_Line1->sidedef[1]->SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
+				m_Line2->sidedef[0]->SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
+				m_Line2->sidedef[1]->SetTexture(side_t::mid, ani.TextureFrames[m_Frame]);
 			}
 		}
 		break;
@@ -686,7 +686,7 @@ DAnimatedDoor::DAnimatedDoor (sector_t *sec, line_t *line, int speed, int delay)
 	// The DMovingCeiling constructor automatically sets up an interpolation for us.
 	// Stop it, since the ceiling is moving instantly here.
 	StopInterpolation();
-	m_WhichDoorIndex = P_FindSlidingDoorType (sides[line->sidenum[0]].GetTexture(side_t::top));
+	m_WhichDoorIndex = P_FindSlidingDoorType (line->sidedef[0]->GetTexture(side_t::top));
 	if (m_WhichDoorIndex < 0)
 	{
 		Printf ("EV_SlidingDoor: Textures are not defined for sliding door!");
@@ -702,16 +702,17 @@ DAnimatedDoor::DAnimatedDoor (sector_t *sec, line_t *line, int speed, int delay)
 		if (sec->lines[i] == line)
 			continue;
 
-		if (sides[sec->lines[i]->sidenum[0]].GetTexture(side_t::top) == sides[line->sidenum[0]].GetTexture(side_t::top))
+		if (sec->lines[i]->sidedef[0]->GetTexture(side_t::top) == line->sidedef[0]->GetTexture(side_t::top))
 		{
 			m_Line2 = sec->lines[i];
 			break;
 		}
 	}
 
-	picnum = sides[m_Line1->sidenum[0]].GetTexture(side_t::top);
-	sides[m_Line1->sidenum[0]].SetTexture(side_t::mid, picnum);
-	sides[m_Line2->sidenum[0]].SetTexture(side_t::mid, picnum);
+
+	picnum = m_Line1->sidedef[0]->GetTexture(side_t::top);
+	m_Line1->sidedef[0]->SetTexture(side_t::mid, picnum);
+	m_Line2->sidedef[0]->SetTexture(side_t::mid, picnum);
 
 	// don't forget texture scaling here!
 	FTexture *tex = TexMan[picnum];
@@ -770,7 +771,7 @@ bool EV_SlidingDoor (line_t *line, AActor *actor, int tag, int speed, int delay)
 			}
 			return false;
 		}
-		if (P_FindSlidingDoorType (sides[line->sidenum[0]].GetTexture(side_t::top)) >= 0)
+		if (P_FindSlidingDoorType (line->sidedef[0]->GetTexture(side_t::top)) >= 0)
 		{
 			new DAnimatedDoor (sec, line, speed, delay);
 			return true;
@@ -793,7 +794,7 @@ bool EV_SlidingDoor (line_t *line, AActor *actor, int tag, int speed, int delay)
 			{
 				continue;
 			}
-			if (P_FindSlidingDoorType (sides[line->sidenum[0]].GetTexture(side_t::top)) >= 0)
+			if (P_FindSlidingDoorType (line->sidedef[0]->GetTexture(side_t::top)) >= 0)
 			{
 				rtn = true;
 				new DAnimatedDoor (sec, line, speed, delay);
diff --git a/src/p_enemy.cpp b/src/p_enemy.cpp
index 0553209e8..1289b6f04 100644
--- a/src/p_enemy.cpp
+++ b/src/p_enemy.cpp
@@ -141,19 +141,19 @@ void P_RecursiveSound (sector_t *sec, AActor *soundtarget, bool splash, int soun
 	for (i = 0; i < sec->linecount; i++)
 	{
 		check = sec->lines[i];
-		if (check->sidenum[1] == NO_SIDE ||
+		if (check->sidedef[1] == NULL ||
 			!(check->flags & ML_TWOSIDED))
 		{
 			continue;
 		}
 		
 		// Early out for intra-sector lines
-		if (sides[check->sidenum[0]].sector==sides[check->sidenum[1]].sector) continue;
+		if (check->sidedef[0]->sector == check->sidedef[1]->sector) continue;
 
-		if ( sides[ check->sidenum[0] ].sector == sec)
-			other = sides[ check->sidenum[1] ].sector;
+		if ( check->sidedef[0]->sector == sec)
+			other = check->sidedef[1]->sector;
 		else
-			other = sides[ check->sidenum[0] ].sector;
+			other = check->sidedef[0]->sector;
 
 		// check for closed door
 		if ((sec->floorplane.ZatPoint (check->v1->x, check->v1->y) >=
diff --git a/src/p_lnspec.cpp b/src/p_lnspec.cpp
index 0c10d9cae..a49843327 100644
--- a/src/p_lnspec.cpp
+++ b/src/p_lnspec.cpp
@@ -1868,7 +1868,7 @@ static void SetWallScroller (int id, int sidechoice, fixed_t dx, fixed_t dy, int
 			int wallnum = scroller->GetWallNum ();
 
 			if (wallnum >= 0 && sides[wallnum].linedef->id == id &&
-				sides[wallnum].linedef->sidenum[sidechoice] == (DWORD)wallnum &&
+				int(sides[wallnum].linedef->sidedef[sidechoice] - sides) == wallnum &&
 				Where == scroller->GetScrollParts())
 			{
 				scroller->Destroy ();
@@ -1887,7 +1887,7 @@ static void SetWallScroller (int id, int sidechoice, fixed_t dx, fixed_t dy, int
 			{
 				if ((collect.RefNum = ((DScroller *)collect.Obj)->GetWallNum ()) != -1 &&
 					sides[collect.RefNum].linedef->id == id &&
-					sides[collect.RefNum].linedef->sidenum[sidechoice] == (DWORD)collect.RefNum &&
+					int(sides[collect.RefNum].linedef->sidedef[sidechoice] - sides) == collect.RefNum &&
 					Where == ((DScroller *)collect.Obj)->GetScrollParts())
 				{
 					((DScroller *)collect.Obj)->SetRate (dx, dy);
@@ -1902,17 +1902,18 @@ static void SetWallScroller (int id, int sidechoice, fixed_t dx, fixed_t dy, int
 		// Now create scrollers for any walls that don't already have them.
 		while ((linenum = P_FindLineFromID (id, linenum)) >= 0)
 		{
-			unsigned int i;
-			for (i = 0; i < numcollected; i++)
+			if (lines[linenum].sidedef[sidechoice] != NULL)
 			{
-				if ((DWORD)Collection[i].RefNum == lines[linenum].sidenum[sidechoice])
-					break;
-			}
-			if (i == numcollected)
-			{
-				if (lines[linenum].sidenum[sidechoice] != NO_SIDE)
+				int sidenum = int(lines[linenum].sidedef[sidechoice] - sides);
+				unsigned int i;
+				for (i = 0; i < numcollected; i++)
 				{
-					new DScroller (DScroller::sc_side, dx, dy, -1, lines[linenum].sidenum[sidechoice], 0, Where);
+					if (Collection[i].RefNum == sidenum)
+						break;
+				}
+				if (i == numcollected)
+				{
+					new DScroller (DScroller::sc_side, dx, dy, -1, sidenum, 0, Where);
 				}
 			}
 		}
@@ -2262,9 +2263,9 @@ FUNC(LS_Line_SetTextureOffset)
 
 	for(int line = -1; (line = P_FindLineFromID (arg0, line)) >= 0; )
 	{
-		if (lines[line].sidenum[arg3] != NO_SIDE)
+		side_t *side = lines[line].sidedef[arg3];
+		if (side != NULL)
 		{
-			side_t *side = &sides[lines[line].sidenum[arg3]];
 
 			if ((arg4&8)==0)
 			{
@@ -2313,10 +2314,9 @@ FUNC(LS_Line_SetTextureScale)
 
 	for(int line = -1; (line = P_FindLineFromID (arg0, line)) >= 0; )
 	{
-		if (lines[line].sidenum[arg3] != NO_SIDE)
+		side_t *side = lines[line].sidedef[arg3];
+		if (side != NULL)
 		{
-			side_t *side = &sides[lines[line].sidenum[arg3]];
-
 			if ((arg4&8)==0)
 			{
 				// set
@@ -2796,8 +2796,8 @@ FUNC(LS_ClearForceField)
 			{
 				line->flags &= ~(ML_BLOCKING|ML_BLOCKEVERYTHING);
 				line->special = 0;
-				sides[line->sidenum[0]].SetTexture(side_t::mid, FNullTextureID());
-				sides[line->sidenum[1]].SetTexture(side_t::mid, FNullTextureID());
+				line->sidedef[0]->SetTexture(side_t::mid, FNullTextureID());
+				line->sidedef[1]->SetTexture(side_t::mid, FNullTextureID());
 			}
 		}
 	}
@@ -2811,11 +2811,11 @@ FUNC(LS_GlassBreak)
 	bool quest1, quest2;
 
 	ln->flags &= ~(ML_BLOCKING|ML_BLOCKEVERYTHING);
-	switched = P_ChangeSwitchTexture (&sides[ln->sidenum[0]], false, 0, &quest1);
+	switched = P_ChangeSwitchTexture (ln->sidedef[0], false, 0, &quest1);
 	ln->special = 0;
-	if (ln->sidenum[1] != NO_SIDE)
+	if (ln->sidedef[1] != NULL)
 	{
-		switched |= P_ChangeSwitchTexture (&sides[ln->sidenum[1]], false, 0, &quest2);
+		switched |= P_ChangeSwitchTexture (ln->sidedef[1], false, 0, &quest2);
 	}
 	else
 	{
diff --git a/src/p_map.cpp b/src/p_map.cpp
index b445d6453..af299eb26 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -3400,7 +3400,7 @@ void P_TraceBleed (int damage, fixed_t x, fixed_t y, fixed_t z, AActor *actor, a
 
 				DImpactDecal::StaticCreate (bloodType,
 					bleedtrace.X, bleedtrace.Y, bleedtrace.Z,
-					sides + bleedtrace.Line->sidenum[bleedtrace.Side],
+					bleedtrace.Line->sidedef[bleedtrace.Side],
 					bleedtrace.ffloor,
 					bloodcolor);
 			}
@@ -5025,7 +5025,7 @@ void SpawnShootDecal (AActor *t1, const FTraceResults &trace)
 	if (decalbase != NULL)
 	{
 		DImpactDecal::StaticCreate (decalbase->GetDecal (),
-			trace.X, trace.Y, trace.Z, sides + trace.Line->sidenum[trace.Side], trace.ffloor);
+			trace.X, trace.Y, trace.Z, trace.Line->sidedef[trace.Side], trace.ffloor);
 	}
 }
 
diff --git a/src/p_maputl.cpp b/src/p_maputl.cpp
index 664fd3cf8..2d8e8a515 100644
--- a/src/p_maputl.cpp
+++ b/src/p_maputl.cpp
@@ -139,7 +139,7 @@ void P_LineOpening (FLineOpening &open, AActor *actor, const line_t *linedef,
 	sector_t *front, *back;
 	fixed_t fc, ff, bc, bf;
 
-	if (linedef->sidenum[1] == NO_SIDE)
+	if (linedef->sidedef[1] == NULL)
 	{
 		// single sided line
 		open.range = 0;
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index f3f076b95..3968f4201 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -1176,9 +1176,9 @@ void P_ExplodeMissile (AActor *mo, line_t *line, AActor *target)
 	if (line != NULL && cl_missiledecals)
 	{
 		int side = P_PointOnLineSide (mo->x, mo->y, line);
-		if (line->sidenum[side] == NO_SIDE)
+		if (line->sidedef[side] == NULL)
 			side ^= 1;
-		if (line->sidenum[side] != NO_SIDE)
+		if (line->sidedef[side] != NULL)
 		{
 			FDecalBase *base = mo->DecalGenerator;
 			if (base != NULL)
@@ -1212,9 +1212,9 @@ void P_ExplodeMissile (AActor *mo, line_t *line, AActor *target)
 
 					F3DFloor * ffloor=NULL;
 #ifdef _3DFLOORS
-					if (line->sidenum[side^1]!=NO_SIDE)
+					if (line->sidedef[side^1] != NULL)
 					{
-						sector_t * backsector=sides[line->sidenum[side^1]].sector;
+						sector_t * backsector = line->sidedef[side^1]->sector;
 						extsector_t::xfloor &xf = backsector->e->XFloor;
 						// find a 3D-floor to stick to
 						for(unsigned int i=0;i<xf.ffloors.Size();i++)
@@ -1234,7 +1234,7 @@ void P_ExplodeMissile (AActor *mo, line_t *line, AActor *target)
 #endif
 
 					DImpactDecal::StaticCreate (base->GetDecal (),
-						x, y, z, sides + line->sidenum[side], ffloor);
+						x, y, z, line->sidedef[side], ffloor);
 				}
 			}
 		}
@@ -1729,7 +1729,7 @@ fixed_t P_XYMovement (AActor *mo, fixed_t scrollx, fixed_t scrolly)
 					if (mo->BlockingLine != NULL &&
 						mo->player && mo->waterlevel && mo->waterlevel < 3 &&
 						(mo->player->cmd.ucmd.forwardmove | mo->player->cmd.ucmd.sidemove) &&
-						mo->BlockingLine->sidenum[1] != NO_SIDE)
+						mo->BlockingLine->sidedef[1] != NULL)
 					{
 						mo->velz = WATER_JUMP_SPEED;
 					}
diff --git a/src/p_plats.cpp b/src/p_plats.cpp
index 48247843b..f93ab503b 100644
--- a/src/p_plats.cpp
+++ b/src/p_plats.cpp
@@ -260,7 +260,7 @@ manual_plat:
 		if (change)
 		{
 			if (line)
-				sec->SetTexture(sector_t::floor, sides[line->sidenum[0]].sector->GetTexture(sector_t::floor));
+				sec->SetTexture(sector_t::floor, line->sidedef[0]->sector->GetTexture(sector_t::floor));
 			if (change == 1)
 				sec->special &= SECRET_MASK;	// Stop damage and other stuff, if any
 		}
diff --git a/src/p_saveg.cpp b/src/p_saveg.cpp
index 33f5ee510..f5edb99a3 100644
--- a/src/p_saveg.cpp
+++ b/src/p_saveg.cpp
@@ -371,10 +371,10 @@ void P_SerializeWorld (FArchive &arc)
 
 		for (j = 0; j < 2; j++)
 		{
-			if (li->sidenum[j] == NO_SIDE)
+			if (li->sidedef[j] == NULL)
 				continue;
 
-			side_t *si = &sides[li->sidenum[j]];
+			side_t *si = li->sidedef[j];
 			arc << si->textures[side_t::top]
 				<< si->textures[side_t::mid]
 				<< si->textures[side_t::bottom]
diff --git a/src/p_sectors.cpp b/src/p_sectors.cpp
index 6f02ea470..dd98faa25 100644
--- a/src/p_sectors.cpp
+++ b/src/p_sectors.cpp
@@ -476,8 +476,8 @@ fixed_t sector_t::FindShortestTextureAround () const
 	{
 		if (lines[i]->flags & ML_TWOSIDED)
 		{
-			CheckShortestTex (sides[lines[i]->sidenum[0]].GetTexture(side_t::bottom), minsize);
-			CheckShortestTex (sides[lines[i]->sidenum[1]].GetTexture(side_t::bottom), minsize);
+			CheckShortestTex (lines[i]->sidedef[0]->GetTexture(side_t::bottom), minsize);
+			CheckShortestTex (lines[i]->sidedef[1]->GetTexture(side_t::bottom), minsize);
 		}
 	}
 	return minsize < FIXED_MAX ? minsize : TexMan[0]->GetHeight() * FRACUNIT;
@@ -502,8 +502,8 @@ fixed_t sector_t::FindShortestUpperAround () const
 	{
 		if (lines[i]->flags & ML_TWOSIDED)
 		{
-			CheckShortestTex (sides[lines[i]->sidenum[0]].GetTexture(side_t::top), minsize);
-			CheckShortestTex (sides[lines[i]->sidenum[1]].GetTexture(side_t::top), minsize);
+			CheckShortestTex (lines[i]->sidedef[0]->GetTexture(side_t::top), minsize);
+			CheckShortestTex (lines[i]->sidedef[1]->GetTexture(side_t::top), minsize);
 		}
 	}
 	return minsize < FIXED_MAX ? minsize : TexMan[0]->GetHeight() * FRACUNIT;
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index b409e591b..f844b01ea 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -188,9 +188,6 @@ TArray<FMapThing> deathmatchstarts (16);
 FMapThing		playerstarts[MAXPLAYERS];
 
 static void P_AllocateSideDefs (int count);
-static void P_SetSideNum (DWORD *sidenum_p, WORD sidenum);
-
-
 
 
 //===========================================================================
@@ -583,7 +580,7 @@ static void SetTexture (side_t *side, int position, const char *name8)
 		{
 			for(int j = 0; j < 2; j++)
 			{
-				if (lines[i].sidenum[j] == (DWORD)(side - sides))
+				if (lines[i].sidedef[j] == side)
 				{
 					Printf("Unknown %s texture '%s' on %s side of linedef %d\n",
 						positionnames[position], name, sidenames[j], i);
@@ -703,7 +700,7 @@ void P_FloodZone (sector_t *sec, int zonenum)
 		line_t *check = sec->lines[i];
 		sector_t *other;
 
-		if (check->sidenum[1] == NO_SIDE || (check->flags & ML_ZONEBOUNDARY))
+		if (check->sidedef[1] == NULL || (check->flags & ML_ZONEBOUNDARY))
 			continue;
 
 		if (check->frontsector == sec)
@@ -790,12 +787,12 @@ void P_LoadZSegs (FileReaderZ &data)
 		segs[i].v1 = &vertexes[v1];
 		segs[i].v2 = &vertexes[v2];
 		segs[i].linedef = ldef = &lines[line];
-		segs[i].sidedef = &sides[ldef->sidenum[side]];
+		segs[i].sidedef = ldef->sidedef[side];
 		segs[i].PartnerSeg = NULL;
-		segs[i].frontsector = sides[ldef->sidenum[side]].sector;
-		if (ldef->flags & ML_TWOSIDED && ldef->sidenum[side^1] != NO_SIDE)
+		segs[i].frontsector = ldef->sidedef[side]->sector;
+		if (ldef->flags & ML_TWOSIDED && ldef->sidedef[side^1] != NULL)
 		{
-			segs[i].backsector = sides[ldef->sidenum[side^1]].sector;
+			segs[i].backsector = ldef->sidedef[side^1]->sector;
 		}
 		else
 		{
@@ -860,11 +857,11 @@ void P_LoadGLZSegs (FileReaderZ &data, DWORD id)
 				line_t *ldef;
 
 				seg->linedef = ldef = &lines[line];
-				seg->sidedef = &sides[ldef->sidenum[side]];
-				seg->frontsector = sides[ldef->sidenum[side]].sector;
-				if (ldef->flags & ML_TWOSIDED && ldef->sidenum[side^1] != NO_SIDE)
+				seg->sidedef = ldef->sidedef[side];
+				seg->frontsector = ldef->sidedef[side]->sector;
+				if (ldef->flags & ML_TWOSIDED && ldef->sidedef[side^1] != NULL)
 				{
-					seg->backsector = sides[ldef->sidenum[side^1]].sector;
+					seg->backsector = ldef->sidedef[side^1]->sector;
 				}
 				else
 				{
@@ -1152,17 +1149,17 @@ void P_LoadSegs (MapData * map)
 			ldef = &lines[linedef];
 			li->linedef = ldef;
 			side = LittleShort(ml->side);
-			if ((unsigned)ldef->sidenum[side] >= (unsigned)numsides)
+			if ((unsigned)(ldef->sidedef[side] - sides) >= (unsigned)numsides)
 			{
 				throw i * 4 + 2;
 			}
-			li->sidedef = &sides[ldef->sidenum[side]];
-			li->frontsector = sides[ldef->sidenum[side]].sector;
+			li->sidedef = ldef->sidedef[side];
+			li->frontsector = ldef->sidedef[side]->sector;
 
 			// killough 5/3/98: ignore 2s flag if second sidedef missing:
-			if (ldef->flags & ML_TWOSIDED && ldef->sidenum[side^1] != NO_SIDE)
+			if (ldef->flags & ML_TWOSIDED && ldef->sidedef[side^1] != NULL)
 			{
-				li->backsector = sides[ldef->sidenum[side^1]].sector;
+				li->backsector = ldef->sidedef[side^1]->sector;
 			}
 			else
 			{
@@ -1718,20 +1715,20 @@ void P_SetLineID (line_t *ld)
 
 void P_SaveLineSpecial (line_t *ld)
 {
-	if (*ld->sidenum == NO_SIDE)
+	if (ld->sidedef[0] == NULL)
 		return;
 
+	DWORD sidenum = DWORD(ld->sidedef[0]-sides);
 	// killough 4/4/98: support special sidedef interpretation below
-	if ((ld->sidenum[0] != NO_SIDE) &&
-		// [RH] Save Static_Init only if it's interested in the textures
-		(ld->special != Static_Init || ld->args[1] == Init_Color))
+	// [RH] Save Static_Init only if it's interested in the textures
+	if	(ld->special != Static_Init || ld->args[1] == Init_Color)
 	{
-		sidetemp[*ld->sidenum].a.special = ld->special;
-		sidetemp[*ld->sidenum].a.tag = ld->args[0];
+		sidetemp[sidenum].a.special = ld->special;
+		sidetemp[sidenum].a.tag = ld->args[0];
 	}
 	else
 	{
-		sidetemp[*ld->sidenum].a.special = 0;
+		sidetemp[sidenum].a.special = 0;
 	}
 }
 
@@ -1739,8 +1736,8 @@ void P_FinishLoadingLineDef(line_t *ld, int alpha)
 {
 	bool additive = false;
 
-	ld->frontsector = ld->sidenum[0]!=NO_SIDE ? sides[ld->sidenum[0]].sector : 0;
-	ld->backsector  = ld->sidenum[1]!=NO_SIDE ? sides[ld->sidenum[1]].sector : 0;
+	ld->frontsector = ld->sidedef[0] != NULL ? ld->sidedef[0]->sector : NULL;
+	ld->backsector  = ld->sidedef[1] != NULL ? ld->sidedef[1]->sector : NULL;
 	float dx = FIXED2FLOAT(ld->v2->x - ld->v1->x);
 	float dy = FIXED2FLOAT(ld->v2->y - ld->v1->y);
 	int linenum = int(ld-lines);
@@ -1753,16 +1750,16 @@ void P_FinishLoadingLineDef(line_t *ld, int alpha)
 	// [RH] Set some new sidedef properties
 	int len = (int)(sqrtf (dx*dx + dy*dy) + 0.5f);
 
-	if (ld->sidenum[0] != NO_SIDE)
+	if (ld->sidedef[0] != NULL)
 	{
-		sides[ld->sidenum[0]].linedef = ld;
-		sides[ld->sidenum[0]].TexelLength = len;
+		ld->sidedef[0]->linedef = ld;
+		ld->sidedef[0]->TexelLength = len;
 
 	}
-	if (ld->sidenum[1] != NO_SIDE)
+	if (ld->sidedef[1] != NULL)
 	{
-		sides[ld->sidenum[1]].linedef = ld;
-		sides[ld->sidenum[1]].TexelLength = len;
+		ld->sidedef[1]->linedef = ld;
+		ld->sidedef[1]->TexelLength = len;
 	}
 
 	switch (ld->special)
@@ -1814,7 +1811,24 @@ void P_FinishLoadingLineDefs ()
 {
 	for (int i = 0; i < numlines; i++)
 	{
-		P_FinishLoadingLineDef(&lines[i], sidetemp[lines[i].sidenum[0]].a.alpha);
+		P_FinishLoadingLineDef(&lines[i], sidetemp[lines[i].sidedef[0]-sides].a.alpha);
+	}
+}
+
+static void P_SetSideNum (side_t **sidenum_p, WORD sidenum)
+{
+	if (sidenum == NO_INDEX)
+	{
+		*sidenum_p = NULL;
+	}
+	else if (sidecount < numsides)
+	{
+		sidetemp[sidecount].a.map = sidenum;
+		*sidenum_p = &sides[sidecount++];
+	}
+	else
+	{
+		I_Error ("%d sidedefs is not enough\n", sidecount);
 	}
 }
 
@@ -1886,8 +1900,8 @@ void P_LoadLineDefs (MapData * map)
 		ld->v2 = &vertexes[LittleShort(mld->v2)];
 		//ld->id = -1;		ID has been assigned in P_TranslateLineDef
 
-		P_SetSideNum (&ld->sidenum[0], LittleShort(mld->sidenum[0]));
-		P_SetSideNum (&ld->sidenum[1], LittleShort(mld->sidenum[1]));
+		P_SetSideNum (&ld->sidedef[0], LittleShort(mld->sidenum[0]));
+		P_SetSideNum (&ld->sidedef[1], LittleShort(mld->sidenum[1]));
 
 		P_AdjustLine (ld);
 		P_SaveLineSpecial (ld);
@@ -1963,8 +1977,8 @@ void P_LoadLineDefs2 (MapData * map)
 		ld->Alpha = FRACUNIT;	// [RH] Opaque by default
 		ld->id = -1;
 
-		P_SetSideNum (&ld->sidenum[0], LittleShort(mld->sidenum[0]));
-		P_SetSideNum (&ld->sidenum[1], LittleShort(mld->sidenum[1]));
+		P_SetSideNum (&ld->sidedef[0], LittleShort(mld->sidenum[0]));
+		P_SetSideNum (&ld->sidedef[1], LittleShort(mld->sidenum[1]));
 
 		P_AdjustLine (ld);
 		P_SetLineID(ld);
@@ -2013,22 +2027,6 @@ static void P_AllocateSideDefs (int count)
 	sidecount = 0;
 }
 
-static void P_SetSideNum (DWORD *sidenum_p, WORD sidenum)
-{
-	if (sidenum == NO_INDEX)
-	{
-		*sidenum_p = NO_SIDE;
-	}
-	else if (sidecount < numsides)
-	{
-		sidetemp[sidecount].a.map = sidenum;
-		*sidenum_p = sidecount++;
-	}
-	else
-	{
-		I_Error ("%d sidedefs is not enough\n", sidecount);
-	}
-}
 
 // [RH] Group sidedefs into loops so that we can easily determine
 // what walls any particular wall neighbors.
@@ -2057,7 +2055,7 @@ static void P_LoopSidedefs ()
 		// For each vertex, build a list of sidedefs that use that vertex
 		// as their left edge.
 		line_t *line = sides[i].linedef;
-		int lineside = (line->sidenum[0] != (DWORD)i);
+		int lineside = (line->sidedef[0] != &sides[i]);
 		int vert = int((lineside ? line->v2 : line->v1) - vertexes);
 		
 		sidetemp[i].b.lineside = lineside;
@@ -2082,7 +2080,7 @@ static void P_LoopSidedefs ()
 		// instead of as part of another loop
 		if (line->frontsector == line->backsector)
 		{
-			right = line->sidenum[!sidetemp[i].b.lineside];
+			right = DWORD(line->sidedef[!sidetemp[i].b.lineside] - sides);
 		}
 		else
 		{
diff --git a/src/p_spec.cpp b/src/p_spec.cpp
index e1145fdf3..d70129d0f 100644
--- a/src/p_spec.cpp
+++ b/src/p_spec.cpp
@@ -234,7 +234,7 @@ bool P_ActivateLine (line_t *line, AActor *mo, int side, int activationType)
 	{
 		if (activationType == SPAC_Use || activationType == SPAC_Impact)
 		{
-			P_ChangeSwitchTexture (&sides[line->sidenum[0]], repeat, special);
+			P_ChangeSwitchTexture (line->sidedef[0], repeat, special);
 		}
 	}
 	// some old WADs use this method to create walls that change the texture when shot.
@@ -247,7 +247,7 @@ bool P_ActivateLine (line_t *line, AActor *mo, int side, int activationType)
 		line->args[0] &&										// only if there's a tag (which is stored in the first arg)
 		P_FindSectorFromTag (line->args[0], -1) == -1)			// only if no sector is tagged to this linedef
 	{
-		P_ChangeSwitchTexture (&sides[line->sidenum[0]], repeat, special);
+		P_ChangeSwitchTexture (line->sidedef[0], repeat, special);
 		line->special = 0;
 	}
 // end of changed code
@@ -778,14 +778,14 @@ DWallLightTransfer::DWallLightTransfer (sector_t *srcSec, int target, BYTE flags
 
 	for (linenum = -1; (linenum = P_FindLineFromID (target, linenum)) >= 0; )
 	{
-		if (flags & WLF_SIDE1 && lines[linenum].sidenum[0]!=NO_SIDE)
+		if (flags & WLF_SIDE1 && lines[linenum].sidedef[0] != NULL)
 		{
-			sides[lines[linenum].sidenum[0]].Flags |= wallflags;
+			lines[linenum].sidedef[0]->Flags |= wallflags;
 		}
 
-		if (flags & WLF_SIDE2 && lines[linenum].sidenum[1]!=NO_SIDE)
+		if (flags & WLF_SIDE2 && lines[linenum].sidedef[1] != NULL)
 		{
-			sides[lines[linenum].sidenum[1]].Flags |= wallflags;
+			lines[linenum].sidedef[1]->Flags |= wallflags;
 		}
 	}
 	ChangeStatNum(STAT_LIGHTTRANSFER);
@@ -810,14 +810,14 @@ void DWallLightTransfer::DoTransfer (BYTE lightlevel, int target, BYTE flags)
 	{
 		line_t * line = &lines[linenum];
 
-		if (flags & WLF_SIDE1 && line->sidenum[0]!=NO_SIDE)
+		if (flags & WLF_SIDE1 && line->sidedef[0] != NULL)
 		{
-			sides[line->sidenum[0]].SetLight(lightlevel);
+			line->sidedef[0]->SetLight(lightlevel);
 		}
 
-		if (flags & WLF_SIDE2 && line->sidenum[1]!=NO_SIDE)
+		if (flags & WLF_SIDE2 && line->sidedef[1] != NULL)
 		{
-			sides[line->sidenum[1]].SetLight(lightlevel);
+			line->sidedef[1]->SetLight(lightlevel);
 		}
 	}
 }
@@ -981,7 +981,7 @@ void P_SpawnSpecials (void)
 		// killough 3/7/98:
 		// support for drawn heights coming from different sector
 		case Transfer_Heights:
-			sec = sides[lines[i].sidenum[0]].sector;
+			sec = lines[i].frontsector;
 			if (lines[i].args[1] & 2)
 			{
 				sec->MoreFlags |= SECF_FAKEFLOORONLY;
@@ -1017,19 +1017,19 @@ void P_SpawnSpecials (void)
 		// killough 3/16/98: Add support for setting
 		// floor lighting independently (e.g. lava)
 		case Transfer_FloorLight:
-			new DLightTransfer (sides[*lines[i].sidenum].sector, lines[i].args[0], true);
+			new DLightTransfer (lines[i].frontsector, lines[i].args[0], true);
 			break;
 
 		// killough 4/11/98: Add support for setting
 		// ceiling lighting independently
 		case Transfer_CeilingLight:
-			new DLightTransfer (sides[*lines[i].sidenum].sector, lines[i].args[0], false);
+			new DLightTransfer (lines[i].frontsector, lines[i].args[0], false);
 			break;
 
 		// [Graf Zahl] Add support for setting lighting
 		// per wall independently
 		case Transfer_WallLight:
-			new DWallLightTransfer (sides[*lines[i].sidenum].sector, lines[i].args[0], lines[i].args[1]);
+			new DWallLightTransfer (lines[i].frontsector, lines[i].args[0], lines[i].args[1]);
 			break;
 
 		case Sector_Attach3dMidtex:
@@ -1290,7 +1290,7 @@ DScroller::DScroller (fixed_t dx, fixed_t dy, const line_t *l,
 	m_Parts = scrollpos;
 	if ((m_Control = control) != -1)
 		m_LastHeight = sectors[control].CenterFloor() + sectors[control].CenterCeiling();
-	m_Affectee = *l->sidenum;
+	m_Affectee = int(l->sidedef[0] - sides);
 	sides[m_Affectee].Flags |= WALLF_NOAUTODECALS;
 	m_Interpolations[0] = m_Interpolations[1] = m_Interpolations[2] = NULL;
 
@@ -1347,7 +1347,7 @@ static void P_SpawnScrollers(void)
 			{
 				// if 1, then displacement
 				// if 2, then accelerative (also if 3)
-				control = int(sides[*l->sidenum].sector - sectors);
+				control = int(l->sidedef[0]->sector - sectors);
 				if (l->args[1] & 2)
 					accel = 1;
 			}
@@ -1400,36 +1400,41 @@ static void P_SpawnScrollers(void)
 
 		case Scroll_Texture_Offsets:
 			// killough 3/2/98: scroll according to sidedef offsets
-			s = lines[i].sidenum[0];
+			s = int(lines[i].sidedef[0] - sides);
 			new DScroller (DScroller::sc_side, -sides[s].GetTextureXOffset(side_t::mid),
 				sides[s].GetTextureYOffset(side_t::mid), -1, s, accel, SCROLLTYPE(l->args[0]));
 			break;
 
 		case Scroll_Texture_Left:
+			s = int(lines[i].sidedef[0] - sides);
 			new DScroller (DScroller::sc_side, l->args[0] * (FRACUNIT/64), 0,
-						   -1, lines[i].sidenum[0], accel, SCROLLTYPE(l->args[1]));
+						   -1, s, accel, SCROLLTYPE(l->args[1]));
 			break;
 
 		case Scroll_Texture_Right:
+			s = int(lines[i].sidedef[0] - sides);
 			new DScroller (DScroller::sc_side, l->args[0] * (-FRACUNIT/64), 0,
-						   -1, lines[i].sidenum[0], accel, SCROLLTYPE(l->args[1]));
+						   -1, s, accel, SCROLLTYPE(l->args[1]));
 			break;
 
 		case Scroll_Texture_Up:
+			s = int(lines[i].sidedef[0] - sides);
 			new DScroller (DScroller::sc_side, 0, l->args[0] * (FRACUNIT/64),
-						   -1, lines[i].sidenum[0], accel, SCROLLTYPE(l->args[1]));
+						   -1, s, accel, SCROLLTYPE(l->args[1]));
 			break;
 
 		case Scroll_Texture_Down:
+			s = int(lines[i].sidedef[0] - sides);
 			new DScroller (DScroller::sc_side, 0, l->args[0] * (-FRACUNIT/64),
-						   -1, lines[i].sidenum[0], accel, SCROLLTYPE(l->args[1]));
+						   -1, s, accel, SCROLLTYPE(l->args[1]));
 			break;
 
 		case Scroll_Texture_Both:
+			s = int(lines[i].sidedef[0] - sides);
 			if (l->args[0] == 0) {
 				dx = (l->args[1] - l->args[2]) * (FRACUNIT/64);
 				dy = (l->args[4] - l->args[3]) * (FRACUNIT/64);
-				new DScroller (DScroller::sc_side, dx, dy, -1, lines[i].sidenum[0], accel);
+				new DScroller (DScroller::sc_side, dx, dy, -1, s, accel);
 			}
 			break;
 
diff --git a/src/p_spec.h b/src/p_spec.h
index f2473f3f1..dbf330082 100644
--- a/src/p_spec.h
+++ b/src/p_spec.h
@@ -195,7 +195,7 @@ void	P_SetSectorFriction (int tag, int amount, bool alterFlag);
 //
 inline side_t *getSide (int currentSector, int line, int side)
 {
-	return &sides[ (sectors[currentSector].lines[line])->sidenum[side] ];
+	return (sectors[currentSector].lines[line])->sidedef[side];
 }
 
 //
@@ -206,7 +206,7 @@ inline side_t *getSide (int currentSector, int line, int side)
 //
 inline sector_t *getSector (int currentSector, int line, int side)
 {
-	return sides[ (sectors[currentSector].lines[line])->sidenum[side] ].sector;
+	return (sectors[currentSector].lines[line])->sidedef[side]->sector;
 }
 
 
diff --git a/src/p_switch.cpp b/src/p_switch.cpp
index cd2b65413..4e312a166 100644
--- a/src/p_switch.cpp
+++ b/src/p_switch.cpp
@@ -465,12 +465,12 @@ static int TryFindSwitch (side_t *side, int Where)
 bool P_CheckSwitchRange(AActor *user, line_t *line, int sideno)
 {
 	// Activated from an empty side -> always succeed
-	if (line->sidenum[sideno] == NO_SIDE) return true;
+	side_t *side = line->sidedef[sideno];
+	if (side == NULL) return true;
 
 	fixed_t checktop;
 	fixed_t checkbot;
-	side_t *side = &sides[line->sidenum[sideno]];
-	sector_t *front = sides[line->sidenum[sideno]].sector;
+	sector_t *front = side->sector;
 	FLineOpening open;
 
 	// 3DMIDTEX forces CHECKSWITCHRANGE because otherwise it might cause problems.
@@ -492,7 +492,7 @@ bool P_CheckSwitchRange(AActor *user, line_t *line, int sideno)
 	checky = dll.y + FixedMul(dll.dy, inter);
 
 	// one sided line
-	if (line->sidenum[1] == NO_SIDE) 
+	if (line->sidedef[1] == NULL) 
 	{
 	onesided:
 		fixed_t sectorc = front->ceilingplane.ZatPoint(checkx, checky);
diff --git a/src/p_teleport.cpp b/src/p_teleport.cpp
index ca75de03d..8fe870e82 100644
--- a/src/p_teleport.cpp
+++ b/src/p_teleport.cpp
@@ -397,7 +397,7 @@ bool EV_SilentLineTeleport (line_t *line, int side, AActor *thing, int id, INTBO
 	int i;
 	line_t *l;
 
-	if (side || thing->flags2 & MF2_NOTELEPORT || !line || line->sidenum[1] == NO_SIDE)
+	if (side || thing->flags2 & MF2_NOTELEPORT || !line || line->sidedef[1] == NULL)
 		return false;
 
 	for (i = -1; (i = P_FindLineFromID (id, i)) >= 0; )
@@ -476,8 +476,8 @@ bool EV_SilentLineTeleport (line_t *line, int side, AActor *thing, int id, INTBO
 			// Height of thing above ground
 			fixed_t z;
 			
-			z = thing->z - sides[line->sidenum[1]].sector->floorplane.ZatPoint (thing->x, thing->y)
-				+ sides[l->sidenum[0]].sector->floorplane.ZatPoint (x, y);
+			z = thing->z - line->backsector->floorplane.ZatPoint (thing->x, thing->y)
+				+ l->frontsector->floorplane.ZatPoint (x, y);
 
 			// Attempt to teleport, aborting if blocked
 			// Adjust z position to be same height above ground as before.
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index dedef053c..b9c41b724 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -599,7 +599,7 @@ struct UDMFParser
 		memset(ld, 0, sizeof(*ld));
 		ld->Alpha = FRACUNIT;
 		ld->id = -1;
-		ld->sidenum[0] = ld->sidenum[1] = NO_SIDE;
+		ld->sidedef[0] = ld->sidedef[1] = NULL;
 		if (level.flags2 & LEVEL2_CLIPMIDTEX) ld->flags |= ML_CLIP_MIDTEX;
 		if (level.flags2 & LEVEL2_WRAPMIDTEX) ld->flags |= ML_WRAP_MIDTEX;
 		if (level.flags2 & LEVEL2_CHECKSWITCHRANGE) ld->flags |= ML_CHECKSWITCHRANGE;
@@ -635,11 +635,11 @@ struct UDMFParser
 				continue;
 
 			case NAME_Sidefront:
-				ld->sidenum[0] = CheckInt(key);
+				ld->sidedef[0] = (side_t*)(intptr_t)(1 + CheckInt(key));
 				continue;
 
 			case NAME_Sideback:
-				ld->sidenum[1] = CheckInt(key);
+				ld->sidedef[1] = (side_t*)(intptr_t)(1 + CheckInt(key));
 				continue;
 
 			case NAME_Arg0:
@@ -1281,9 +1281,9 @@ struct UDMFParser
 				ParsedLines[i].v1 = &vertexes[v1i];
 				ParsedLines[i].v2 = &vertexes[v2i];
 
-				if (ParsedLines[i].sidenum[0] != NO_SIDE)
+				if (ParsedLines[i].sidedef[0] != NULL)
 					sidecount++;
-				if (ParsedLines[i].sidenum[1] != NO_SIDE)
+				if (ParsedLines[i].sidedef[1] != NULL)
 					sidecount++;
 				linemap.Push(i+skipped);
 				i++;
@@ -1302,13 +1302,13 @@ struct UDMFParser
 
 			for(int sd = 0; sd < 2; sd++)
 			{
-				if (lines[line].sidenum[sd] != NO_SIDE)
+				if (lines[line].sidedef[sd] != NULL)
 				{
-					int mapside = lines[line].sidenum[sd];
+					int mapside = int(intptr_t(lines[line].sidedef[sd]))-1;
 					sides[side] = ParsedSides[mapside];
 					sides[side].linedef = &lines[line];
 					sides[side].sector = &sectors[intptr_t(sides[side].sector)];
-					lines[line].sidenum[sd] = side;
+					lines[line].sidedef[sd] = &sides[side];
 
 					P_ProcessSideTextures(!isExtended, &sides[side], sides[side].sector, &ParsedSideTextures[mapside],
 						lines[line].special, lines[line].args[0], &tempalpha[sd]);
diff --git a/src/p_writemap.cpp b/src/p_writemap.cpp
index 9261ee904..db758631f 100644
--- a/src/p_writemap.cpp
+++ b/src/p_writemap.cpp
@@ -121,8 +121,8 @@ static int WriteLINEDEFS (FILE *file)
 		{
 			mld.args[j] = (BYTE)lines[i].args[j];
 		}
-		mld.sidenum[0] = LittleShort(WORD(lines[i].sidenum[0]));
-		mld.sidenum[1] = LittleShort(WORD(lines[i].sidenum[1]));
+		mld.sidenum[0] = LittleShort(WORD(lines[i].sidedef[0] - sides));
+		mld.sidenum[1] = LittleShort(WORD(lines[i].sidedef[1] - sides));
 		fwrite (&mld, sizeof(mld), 1, file);
 	}
 	return numlines * sizeof(mld);
@@ -184,7 +184,7 @@ static int WriteSEGS (FILE *file)
 			ms.v1 = LittleShort(short(segs[i].v1 - vertexes));
 			ms.v2 = LittleShort(short(segs[i].v2 - vertexes));
 			ms.linedef = LittleShort(short(segs[i].linedef - lines));
-			ms.side = DWORD(segs[i].sidedef - sides) == segs[i].linedef->sidenum[0] ? 0 : LittleShort((short)1);
+			ms.side = segs[i].sidedef == segs[i].linedef->sidedef[0] ? 0 : LittleShort((short)1);
 			ms.angle = LittleShort(short(R_PointToAngle2 (segs[i].v1->x, segs[i].v1->y, segs[i].v2->x, segs[i].v2->y)>>16));
 			fwrite (&ms, sizeof(ms), 1, file);
 		}
diff --git a/src/r_bsp.cpp b/src/r_bsp.cpp
index ffb8a1f4f..bf09603e3 100644
--- a/src/r_bsp.cpp
+++ b/src/r_bsp.cpp
@@ -648,7 +648,7 @@ void R_AddLine (seg_t *line)
 	}
 	else
 	{ // The seg is only part of the wall.
-		if (line->linedef->sidenum[0] != DWORD(line->sidedef - sides))
+		if (line->linedef->sidedef[0] != line->sidedef)
 		{
 			swap (v1, v2);
 		}
diff --git a/src/r_defs.h b/src/r_defs.h
index b4361adc3..cf287de20 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -872,7 +872,8 @@ struct line_t
 	int			id;			// <--- same as tag or set with Line_SetIdentification
 	int			args[5];	// <--- hexen-style arguments (expanded to ZDoom's full width)
 	int			firstid, nextid;
-	DWORD		sidenum[2];	// sidenum[1] will be NO_SIDE if one sided
+	side_t		*sidedef[2];
+	//DWORD		sidenum[2];	// sidenum[1] will be NO_SIDE if one sided
 	fixed_t		bbox[4];	// bounding box, for the extent of the LineDef.
 	slopetype_t	slopetype;	// To aid move clipping.
 	sector_t	*frontsector, *backsector;
diff --git a/src/r_plane.cpp b/src/r_plane.cpp
index 9be0b0b5d..b2dc9ac40 100644
--- a/src/r_plane.cpp
+++ b/src/r_plane.cpp
@@ -1290,7 +1290,7 @@ void R_DrawSkyPlane (visplane_t *pl)
 			const line_t *l = &lines[(pl->sky & ~PL_SKYFLAT)-1];
 
 			// Sky transferred from first sidedef
-			const side_t *s = *l->sidenum + sides;
+			const side_t *s = l->sidedef[0];
 			int pos;
 
 			// Texture comes from upper texture of reference sidedef
diff --git a/src/r_polymost.cpp b/src/r_polymost.cpp
index 57a315391..f5f82950a 100644
--- a/src/r_polymost.cpp
+++ b/src/r_polymost.cpp
@@ -1202,7 +1202,7 @@ void RP_AddLine (seg_t *line)
 	}
 	else
 	{ // The seg is only part of the wall.
-		if (line->linedef->sidenum[0] != DWORD(line->sidedef - sides))
+		if (line->linedef->sidedef[0] != line->sidedef)
 		{
 			swap (v1, v2);
 		}