diff --git a/src/dobject.cpp b/src/dobject.cpp
index 191fa3c43..9d674d226 100644
--- a/src/dobject.cpp
+++ b/src/dobject.cpp
@@ -517,8 +517,8 @@ size_t DObject::StaticPointerSubstitution (DObject *old, DObject *notOld)
 #define SECTOR_CHECK(f,t) \
 	if (sectors[i].f.p == static_cast<t *>(old)) { sectors[i].f = static_cast<t *>(notOld); changed++; }
 			SECTOR_CHECK( SoundTarget, AActor );
-			SECTOR_CHECK( CeilingSkyBox, ASkyViewpoint );
-			SECTOR_CHECK( FloorSkyBox, ASkyViewpoint );
+			SECTOR_CHECK( SkyBoxes[sector_t::ceiling], ASkyViewpoint );
+			SECTOR_CHECK( SkyBoxes[sector_t::floor], ASkyViewpoint );
 			SECTOR_CHECK( SecActTarget, ASectorAction );
 			SECTOR_CHECK( floordata, DSectorEffect );
 			SECTOR_CHECK( ceilingdata, DSectorEffect );
diff --git a/src/dobjgc.cpp b/src/dobjgc.cpp
index d52962f11..3812c0b08 100644
--- a/src/dobjgc.cpp
+++ b/src/dobjgc.cpp
@@ -640,8 +640,8 @@ size_t DSectorMarker::PropagateMark()
 		{
 			sector_t *sec = &sectors[SecNum + i];
 			GC::Mark(sec->SoundTarget);
-			GC::Mark(sec->CeilingSkyBox);
-			GC::Mark(sec->FloorSkyBox);
+			GC::Mark(sec->SkyBoxes[sector_t::ceiling]);
+			GC::Mark(sec->SkyBoxes[sector_t::floor]);
 			GC::Mark(sec->SecActTarget);
 			GC::Mark(sec->floordata);
 			GC::Mark(sec->ceilingdata);
diff --git a/src/g_shared/a_skies.cpp b/src/g_shared/a_skies.cpp
index ef5623746..a8c8ebd55 100644
--- a/src/g_shared/a_skies.cpp
+++ b/src/g_shared/a_skies.cpp
@@ -67,13 +67,13 @@ void ASkyViewpoint::Destroy ()
 	// remove all sector references to ourselves.
 	for (int i = 0; i <numsectors; i++)
 	{
-		if (sectors[i].FloorSkyBox == this)
+		if (sectors[i].SkyBoxes[sector_t::floor] == this)
 		{
-			sectors[i].FloorSkyBox = NULL;
+			sectors[i].SkyBoxes[sector_t::floor] = NULL;
 		}
-		if (sectors[i].CeilingSkyBox == this)
+		if (sectors[i].SkyBoxes[sector_t::ceiling] == this)
 		{
-			sectors[i].CeilingSkyBox = NULL;
+			sectors[i].SkyBoxes[sector_t::ceiling] = NULL;
 		}
 	}
 	if (level.DefaultSkybox == this)
@@ -129,12 +129,12 @@ void ASkyPicker::PostBeginPlay ()
 	{
 		if (0 == (args[1] & 2))
 		{
-			Sector->CeilingSkyBox = box;
+			Sector->SkyBoxes[sector_t::ceiling] = box;
 			if (box == NULL) Sector->MoreFlags |= SECF_NOCEILINGSKYBOX;	// sector should ignore the level's default skybox
 		}
 		if (0 == (args[1] & 1))
 		{
-			Sector->FloorSkyBox = box;
+			Sector->SkyBoxes[sector_t::floor] = box;
 			if (box == NULL) Sector->MoreFlags |= SECF_NOFLOORSKYBOX;	// sector should ignore the level's default skybox
 		}
 	}
diff --git a/src/p_saveg.cpp b/src/p_saveg.cpp
index db14aeb90..7623104d7 100644
--- a/src/p_saveg.cpp
+++ b/src/p_saveg.cpp
@@ -418,7 +418,7 @@ void P_SerializeWorld (FArchive &arc)
 			<< sec->sky
 			<< sec->MoreFlags
 			<< sec->Flags
-			<< sec->FloorSkyBox << sec->CeilingSkyBox
+			<< sec->SkyBoxes[sector_t::floor] << sec->SkyBoxes[sector_t::ceiling]
 			<< sec->ZoneNumber;
 		if (SaveVersion < 4529)
 		{
diff --git a/src/p_sectors.cpp b/src/p_sectors.cpp
index 6c5c08a56..83adc438f 100644
--- a/src/p_sectors.cpp
+++ b/src/p_sectors.cpp
@@ -805,16 +805,8 @@ int sector_t::GetCeilingLight () const
 
 ASkyViewpoint *sector_t::GetSkyBox(int which)
 {
-	if (which == floor)
-	{
-		if (FloorSkyBox != NULL) return FloorSkyBox;
-		if (MoreFlags & SECF_NOFLOORSKYBOX) return NULL;
-	}
-	else
-	{
-		if (CeilingSkyBox != NULL) return CeilingSkyBox;
-		if (MoreFlags & SECF_NOCEILINGSKYBOX) return NULL;
-	}
+	if (SkyBoxes[which] != NULL) return SkyBoxes[which];
+	if (MoreFlags & (SECF_NOFLOORSKYBOX << which)) return NULL;
 	return level.DefaultSkybox;
 }
 
diff --git a/src/p_spec.cpp b/src/p_spec.cpp
index 08a43fe2a..36d5f3bab 100644
--- a/src/p_spec.cpp
+++ b/src/p_spec.cpp
@@ -909,10 +909,10 @@ static void SetupFloorPortal (AStackPoint *point)
 {
 	NActorIterator it (NAME_LowerStackLookOnly, point->tid);
 	sector_t *Sector = point->Sector;
-	Sector->FloorSkyBox = static_cast<ASkyViewpoint*>(it.Next());
-	if (Sector->FloorSkyBox != NULL && Sector->FloorSkyBox->bAlways)
+	Sector->SkyBoxes[sector_t::floor] = static_cast<ASkyViewpoint*>(it.Next());
+	if (Sector->SkyBoxes[sector_t::floor] != NULL && Sector->SkyBoxes[sector_t::floor]->bAlways)
 	{
-		Sector->FloorSkyBox->Mate = point;
+		Sector->SkyBoxes[sector_t::floor]->Mate = point;
 		if (Sector->GetAlpha(sector_t::floor) == OPAQUE)
 			Sector->SetAlpha(sector_t::floor, Scale (point->args[0], OPAQUE, 255));
 	}
@@ -922,48 +922,15 @@ static void SetupCeilingPortal (AStackPoint *point)
 {
 	NActorIterator it (NAME_UpperStackLookOnly, point->tid);
 	sector_t *Sector = point->Sector;
-	Sector->CeilingSkyBox = static_cast<ASkyViewpoint*>(it.Next());
-	if (Sector->CeilingSkyBox != NULL && Sector->CeilingSkyBox->bAlways)
+	Sector->SkyBoxes[sector_t::ceiling] = static_cast<ASkyViewpoint*>(it.Next());
+	if (Sector->SkyBoxes[sector_t::ceiling] != NULL && Sector->SkyBoxes[sector_t::ceiling]->bAlways)
 	{
-		Sector->CeilingSkyBox->Mate = point;
+		Sector->SkyBoxes[sector_t::ceiling]->Mate = point;
 		if (Sector->GetAlpha(sector_t::ceiling) == OPAQUE)
 			Sector->SetAlpha(sector_t::ceiling, Scale (point->args[0], OPAQUE, 255));
 	}
 }
 
-static bool SpreadCeilingPortal(AStackPoint *pt, fixed_t alpha, sector_t *sector)
-{
-	bool fail = false;
-	sector->validcount = validcount;
-	for(int i=0; i<sector->linecount; i++)
-	{
-		line_t *line = sector->lines[i];
-		sector_t *backsector = sector == line->frontsector? line->backsector : line->frontsector;
-		if (line->backsector == line->frontsector) continue;
-		if (backsector == NULL) { fail = true; continue; }
-		if (backsector->validcount == validcount) continue;
-		if (backsector->CeilingSkyBox == pt) continue;
-
-		// Check if the backside would map to the same visplane
-		if (backsector->CeilingSkyBox != NULL) { fail = true; continue; }
-		if (backsector->ceilingplane != sector->ceilingplane) { fail = true; continue; }
-		if (backsector->lightlevel != sector->lightlevel) { fail = true; continue; }
-		if (backsector->GetTexture(sector_t::ceiling)		!= sector->GetTexture(sector_t::ceiling)) { fail = true; continue; }
-		if (backsector->GetXOffset(sector_t::ceiling)		!= sector->GetXOffset(sector_t::ceiling)) { fail = true; continue; }
-		if (backsector->GetYOffset(sector_t::ceiling)		!= sector->GetYOffset(sector_t::ceiling)) { fail = true; continue; }
-		if (backsector->GetXScale(sector_t::ceiling)		!= sector->GetXScale(sector_t::ceiling)) { fail = true; continue; }
-		if (backsector->GetYScale(sector_t::ceiling)		!= sector->GetYScale(sector_t::ceiling)) { fail = true; continue; }
-		if (backsector->GetAngle(sector_t::ceiling)		!= sector->GetAngle(sector_t::ceiling)) { fail = true; continue; }
-		if (SpreadCeilingPortal(pt, alpha, backsector)) { fail = true; continue; }
-	}
-	if (!fail) 
-	{
-		sector->CeilingSkyBox = pt;
-		sector->SetAlpha(sector_t::ceiling, alpha);
-	}
-	return fail;
-}
-
 void P_SetupPortals()
 {
 	TThinkerIterator<AStackPoint> it;
@@ -991,9 +958,9 @@ static void SetPortal(sector_t *sector, int plane, ASkyViewpoint *portal, fixed_
 	// plane: 0=floor, 1=ceiling, 2=both
 	if (plane > 0)
 	{
-		if (sector->CeilingSkyBox == NULL || !sector->CeilingSkyBox->bAlways) 
+		if (sector->SkyBoxes[sector_t::ceiling] == NULL || !sector->SkyBoxes[sector_t::ceiling]->bAlways) 
 		{
-			sector->CeilingSkyBox = portal;
+			sector->SkyBoxes[sector_t::ceiling] = portal;
 			if (sector->GetAlpha(sector_t::ceiling) == OPAQUE)
 				sector->SetAlpha(sector_t::ceiling, alpha);
 
@@ -1002,9 +969,9 @@ static void SetPortal(sector_t *sector, int plane, ASkyViewpoint *portal, fixed_
 	}
 	if (plane == 2 || plane == 0)
 	{
-		if (sector->FloorSkyBox == NULL || !sector->FloorSkyBox->bAlways) 
+		if (sector->SkyBoxes[sector_t::floor] == NULL || !sector->SkyBoxes[sector_t::floor]->bAlways) 
 		{
-			sector->FloorSkyBox = portal;
+			sector->SkyBoxes[sector_t::floor] = portal;
 		}
 		if (sector->GetAlpha(sector_t::floor) == OPAQUE)
 			sector->SetAlpha(sector_t::floor, alpha);
diff --git a/src/r_defs.h b/src/r_defs.h
index a7e37f369..05fd7bd03 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -346,7 +346,7 @@ enum
 	SECF_DRAWN			= 128,	// sector has been drawn at least once
 	SECF_HIDDEN			= 256,	// Do not draw on textured automap
 	SECF_NOFLOORSKYBOX	= 512,	// force use of regular sky 
-	SECF_NOCEILINGSKYBOX	= 1024,	// force use of regular sky 
+	SECF_NOCEILINGSKYBOX	= 1024,	// force use of regular sky (do not separate from NOFLOORSKYBOX!!!)
 };
 
 enum
@@ -790,7 +790,7 @@ struct sector_t
 
 	// [RH] The sky box to render for this sector. NULL means use a
 	// regular sky.
-	TObjPtr<ASkyViewpoint> FloorSkyBox, CeilingSkyBox;
+	TObjPtr<ASkyViewpoint> SkyBoxes[2];
 
 	int							sectornum;			// for comparing sector copies