diff --git a/src/compatibility.cpp b/src/compatibility.cpp
index 994a34b44..75729ff61 100644
--- a/src/compatibility.cpp
+++ b/src/compatibility.cpp
@@ -116,6 +116,7 @@ static FCompatOption Options[] =
 	{ "corpsegibs",				COMPATF_CORPSEGIBS, 0 },
 	{ "noblockfriends",			COMPATF_NOBLOCKFRIENDS, 0 },
 	{ "spritesort",				COMPATF_SPRITESORT, 0 },
+	{ "hitscan",				COMPATF_HITSCAN, 0 },
 	{ NULL, 0, 0 }
 };
 
diff --git a/src/d_main.cpp b/src/d_main.cpp
index fe560c3c3..ceba6cfff 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -500,7 +500,8 @@ CUSTOM_CVAR(Int, compatmode, 0, CVAR_ARCHIVE|CVAR_NOINITCALL)
 	case 2:	// same as 1 but stricter (NO_PASSMOBJ and INVISIBILITY are also set)
 		v = COMPATF_SHORTTEX|COMPATF_STAIRINDEX|COMPATF_USEBLOCKING|COMPATF_NODOORLIGHT|COMPATF_SPRITESORT|
 			COMPATF_TRACE|COMPATF_MISSILECLIP|COMPATF_SOUNDTARGET|COMPATF_NO_PASSMOBJ|COMPATF_LIMITPAIN|
-			COMPATF_DEHHEALTH|COMPATF_INVISIBILITY|COMPATF_CROSSDROPOFF|COMPATF_CORPSEGIBS;
+			COMPATF_DEHHEALTH|COMPATF_INVISIBILITY|COMPATF_CROSSDROPOFF|COMPATF_CORPSEGIBS|COMPATF_HITSCAN|
+			COMPATF_WALLRUN|COMPATF_NOTOSSDROPS;
 		break;
 
 	case 3: // Boom compat mode
@@ -516,6 +517,11 @@ CUSTOM_CVAR(Int, compatmode, 0, CVAR_ARCHIVE|CVAR_NOINITCALL)
 			COMPATF_MBFMONSTERMOVE|COMPATF_NOBLOCKFRIENDS;
 		break;
 
+	case 6:	// Boom with some added settings to reenable spme 'broken' behavior
+		v = COMPATF_TRACE|COMPATF_SOUNDTARGET|COMPATF_BOOMSCROLL|COMPATF_MISSILECLIP|COMPATF_NO_PASSMOBJ|
+			COMPATF_INVISIBILITY|COMPATF_CORPSEGIBS|COMPATF_HITSCAN|COMPATF_WALLRUN|COMPATF_NOTOSSDROPS;
+		break;
+
 	}
 	compatflags = v;
 }
@@ -548,6 +554,7 @@ CVAR (Flag, compat_mbfmonstermove,compatflags, COMPATF_MBFMONSTERMOVE);
 CVAR (Flag, compat_corpsegibs,	compatflags, COMPATF_CORPSEGIBS);
 CVAR (Flag, compat_noblockfriends,compatflags,COMPATF_NOBLOCKFRIENDS);
 CVAR (Flag, compat_spritesort,	compatflags,COMPATF_SPRITESORT);
+CVAR (Flag, compat_hitscan,		compatflags,COMPATF_HITSCAN);
 
 //==========================================================================
 //
diff --git a/src/doomdef.h b/src/doomdef.h
index 42636f9cb..bfba79a2d 100644
--- a/src/doomdef.h
+++ b/src/doomdef.h
@@ -325,6 +325,7 @@ enum
 	COMPATF_CORPSEGIBS		= 1 << 25,	// Crushed monsters are turned into gibs, rather than replaced by gibs.
 	COMPATF_NOBLOCKFRIENDS	= 1 << 26,	// Friendly monsters aren't blocked by monster-blocking lines.
 	COMPATF_SPRITESORT		= 1 << 27,	// Invert sprite sorting order for sprites of equal distance
+	COMPATF_HITSCAN			= 1 << 28,	// Hitscans use original blockmap anf hit check code.
 };
 
 // Emulate old bugs for select maps. These are not exposed by a cvar
diff --git a/src/m_options.cpp b/src/m_options.cpp
index 50d7966cd..a71b58025 100644
--- a/src/m_options.cpp
+++ b/src/m_options.cpp
@@ -149,13 +149,14 @@ value_t OffOn[2] = {
 	{ 1.0, "Off" }
 };
 
-value_t CompatModes[6] = {
+value_t CompatModes[] = {
 	{ 0.0, "Default" },
 	{ 1.0, "Doom" },
 	{ 2.0, "Doom (strict)" },
 	{ 3.0, "Boom" },
-	{ 4.0, "ZDoom 2.0.63" },
+	{ 6.0, "Boom (strict)" },
 	{ 5.0, "MBF" },
+	{ 4.0, "ZDoom 2.0.63" },
 };
 
 menu_t  *CurrentMenu;
@@ -1092,7 +1093,7 @@ static menu_t DMFlagsMenu =
  *=======================================*/
 
 static menuitem_t CompatibilityItems[] = {
-	{ discrete, "Compatibility mode",						{&compatmode},	{6.0}, {1.0},	{0.0}, {CompatModes} },
+	{ discrete, "Compatibility mode",						{&compatmode},	{7.0}, {1.0},	{0.0}, {CompatModes} },
 	{ redtext,	" ",					{NULL},			{0.0}, {0.0}, {0.0}, {NULL} },
 	{ bitflag,	"Find shortest textures like Doom",			{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_SHORTTEX} },
 	{ bitflag,	"Use buggier stair building",				{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_STAIRINDEX} },
@@ -1122,6 +1123,7 @@ static menuitem_t CompatibilityItems[] = {
 	{ bitflag,	"Crushed monsters can be resurrected",		{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_CORPSEGIBS} },
 	{ bitflag,	"Friendly monsters aren't blocked",			{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_NOBLOCKFRIENDS} },
 	{ bitflag,	"Invert sprite sorting",					{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_SPRITESORT} },
+	{ bitflag,	"Use Doom code for hitscan checks",			{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_HITSCAN} },
 	
 	{ discrete, "Interpolate monster movement",	{&nomonsterinterpolation},		{2.0}, {0.0},	{0.0}, {NoYes} },
 };
diff --git a/src/p_map.cpp b/src/p_map.cpp
index 09d1f944a..4e78227f5 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -2183,48 +2183,53 @@ void FSlide::HitSlideLine (line_t* ld)
 	}																//   ^
 	else															//   |
 	{																// phares
-#if 0
-		fixed_t newlen;
-	
-		if (deltaangle > ANG180)
-			deltaangle += ANG180;
-		//	I_Error ("SlideLine: ang>ANG180");
-
-		lineangle >>= ANGLETOFINESHIFT;
-		deltaangle >>= ANGLETOFINESHIFT;
-
-		newlen = FixedMul (movelen, finecosine[deltaangle]);
-
-		tmxmove = FixedMul (newlen, finecosine[lineangle]);
-		tmymove = FixedMul (newlen, finesine[lineangle]);
-#else
-		divline_t dll, dlv;
-		fixed_t inter1, inter2, inter3;
-
-		P_MakeDivline (ld, &dll);
-
-		dlv.x = slidemo->x;
-		dlv.y = slidemo->y;
-		dlv.dx = dll.dy;
-		dlv.dy = -dll.dx;
-
-		inter1 = P_InterceptVector(&dll, &dlv);
-
-		dlv.dx = tmxmove;
-		dlv.dy = tmymove;
-		inter2 = P_InterceptVector (&dll, &dlv);
-		inter3 = P_InterceptVector (&dlv, &dll);
-
-		if (inter3 != 0)
+		// Doom's original algorithm here does not work well due to imprecisions of the sine table.
+		// However, keep it active if the wallrunning compatibility flag is on
+		if (i_compatflags & COMPATF_WALLRUN)
 		{
-			tmxmove = Scale (inter2-inter1, dll.dx, inter3);
-			tmymove = Scale (inter2-inter1, dll.dy, inter3);
+			fixed_t newlen;
+		
+			if (deltaangle > ANG180)
+				deltaangle += ANG180;
+			//	I_Error ("SlideLine: ang>ANG180");
+
+			lineangle >>= ANGLETOFINESHIFT;
+			deltaangle >>= ANGLETOFINESHIFT;
+
+			newlen = FixedMul (movelen, finecosine[deltaangle]);
+
+			tmxmove = FixedMul (newlen, finecosine[lineangle]);
+			tmymove = FixedMul (newlen, finesine[lineangle]);
 		}
 		else
 		{
-			tmxmove = tmymove = 0;
+			divline_t dll, dlv;
+			fixed_t inter1, inter2, inter3;
+
+			P_MakeDivline (ld, &dll);
+
+			dlv.x = slidemo->x;
+			dlv.y = slidemo->y;
+			dlv.dx = dll.dy;
+			dlv.dy = -dll.dx;
+
+			inter1 = P_InterceptVector(&dll, &dlv);
+
+			dlv.dx = tmxmove;
+			dlv.dy = tmymove;
+			inter2 = P_InterceptVector (&dll, &dlv);
+			inter3 = P_InterceptVector (&dlv, &dll);
+
+			if (inter3 != 0)
+			{
+				tmxmove = Scale (inter2-inter1, dll.dx, inter3);
+				tmymove = Scale (inter2-inter1, dll.dy, inter3);
+			}
+			else
+			{
+				tmxmove = tmymove = 0;
+			}
 		}
-#endif
 	}																// phares
 }
 
diff --git a/src/p_maputl.cpp b/src/p_maputl.cpp
index d4ea1bdf9..fc0197183 100644
--- a/src/p_maputl.cpp
+++ b/src/p_maputl.cpp
@@ -970,81 +970,136 @@ void FPathTraverse::AddThingIntercepts (int bx, int by, FBlockThingsIterator &it
 		divline_t line;
 		int i;
 
-		// [RH] Don't check a corner to corner crossection for hit.
-		// Instead, check against the actual bounding box.
 
-		// There's probably a smarter way to determine which two sides
-		// of the thing face the trace than by trying all four sides...
-		for (i = 0; i < 4; ++i)
+		if (!(i_compatflags & COMPATF_HITSCAN))
 		{
-			switch (i)
+			// [RH] Don't check a corner to corner crossection for hit.
+			// Instead, check against the actual bounding box (but not if compatibility optioned.)
+
+			// There's probably a smarter way to determine which two sides
+			// of the thing face the trace than by trying all four sides...
+			for (i = 0; i < 4; ++i)
 			{
-			case 0:		// Top edge
-				line.x = thing->x + thing->radius;
-				line.y = thing->y + thing->radius;
-				line.dx = -thing->radius * 2;
-				line.dy = 0;
-				break;
-
-			case 1:		// Right edge
-				line.x = thing->x + thing->radius;
-				line.y = thing->y - thing->radius;
-				line.dx = 0;
-				line.dy = thing->radius * 2;
-				break;
-
-			case 2:		// Bottom edge
-				line.x = thing->x - thing->radius;
-				line.y = thing->y - thing->radius;
-				line.dx = thing->radius * 2;
-				line.dy = 0;
-				break;
-
-			case 3:		// Left edge
-				line.x = thing->x - thing->radius;
-				line.y = thing->y + thing->radius;
-				line.dx = 0;
-				line.dy = thing->radius * -2;
-				break;
-			}
-			// Check if this side is facing the trace origin
-			if (P_PointOnDivlineSide (trace.x, trace.y, &line) == 0)
-			{
-				numfronts++;
-
-				// If it is, see if the trace crosses it
-				if (P_PointOnDivlineSide (line.x, line.y, &trace) !=
-					P_PointOnDivlineSide (line.x + line.dx, line.y + line.dy, &trace))
+				switch (i)
 				{
-					// It's a hit
-					fixed_t frac = P_InterceptVector (&trace, &line);
-					if (frac < 0)
-					{ // behind source
+				case 0:		// Top edge
+					line.x = thing->x + thing->radius;
+					line.y = thing->y + thing->radius;
+					line.dx = -thing->radius * 2;
+					line.dy = 0;
+					break;
+
+				case 1:		// Right edge
+					line.x = thing->x + thing->radius;
+					line.y = thing->y - thing->radius;
+					line.dx = 0;
+					line.dy = thing->radius * 2;
+					break;
+
+				case 2:		// Bottom edge
+					line.x = thing->x - thing->radius;
+					line.y = thing->y - thing->radius;
+					line.dx = thing->radius * 2;
+					line.dy = 0;
+					break;
+
+				case 3:		// Left edge
+					line.x = thing->x - thing->radius;
+					line.y = thing->y + thing->radius;
+					line.dx = 0;
+					line.dy = thing->radius * -2;
+					break;
+				}
+				// Check if this side is facing the trace origin
+				if (P_PointOnDivlineSide (trace.x, trace.y, &line) == 0)
+				{
+					numfronts++;
+
+					// If it is, see if the trace crosses it
+					if (P_PointOnDivlineSide (line.x, line.y, &trace) !=
+						P_PointOnDivlineSide (line.x + line.dx, line.y + line.dy, &trace))
+					{
+						// It's a hit
+						fixed_t frac = P_InterceptVector (&trace, &line);
+						if (frac < 0)
+						{ // behind source
+							continue;
+						}
+
+						intercept_t newintercept;
+						newintercept.frac = frac;
+						newintercept.isaline = false;
+						newintercept.done = false;
+						newintercept.d.thing = thing;
+						intercepts.Push (newintercept);
 						continue;
 					}
+				}
+			}
 
+			// If none of the sides was facing the trace, then the trace
+			// must have started inside the box, so add it as an intercept.
+			if (numfronts == 0)
+			{
+				intercept_t newintercept;
+				newintercept.frac = 0;
+				newintercept.isaline = false;
+				newintercept.done = false;
+				newintercept.d.thing = thing;
+				intercepts.Push (newintercept);
+			}
+		}
+		else
+		{
+			// Old code for compatibility purposes
+			fixed_t 		x1, y1, x2, y2;
+			int 			s1, s2;
+			divline_t		dl;
+			fixed_t 		frac;
+				
+			bool tracepositive = (trace.dx ^ trace.dy)>0;
+						
+			// check a corner to corner crossection for hit
+			if (tracepositive)
+			{
+				x1 = thing->x - thing->radius;
+				y1 = thing->y + thing->radius;
+						
+				x2 = thing->x + thing->radius;
+				y2 = thing->y - thing->radius;					
+			}
+			else
+			{
+				x1 = thing->x - thing->radius;
+				y1 = thing->y - thing->radius;
+						
+				x2 = thing->x + thing->radius;
+				y2 = thing->y + thing->radius;					
+			}
+			
+			s1 = P_PointOnDivlineSide (x1, y1, &trace);
+			s2 = P_PointOnDivlineSide (x2, y2, &trace);
+
+			if (s1 != s2)
+			{
+				dl.x = x1;
+				dl.y = y1;
+				dl.dx = x2-x1;
+				dl.dy = y2-y1;
+				
+				frac = P_InterceptVector (&trace, &dl);
+
+				if (frac >= 0)
+				{
 					intercept_t newintercept;
 					newintercept.frac = frac;
 					newintercept.isaline = false;
 					newintercept.done = false;
 					newintercept.d.thing = thing;
 					intercepts.Push (newintercept);
-					continue;
 				}
 			}
 		}
-
-		// If none of the sides was facing the trace, then the trace
-		// must have started inside the box, so add it as an intercept.
-		if (numfronts == 0)
-		{
-			intercept_t newintercept;
-			newintercept.frac = 0;
-			newintercept.isaline = false;
-			newintercept.done = false;
-			newintercept.d.thing = thing;
-			intercepts.Push (newintercept);
-		}
 	}
 }