diff --git a/src/nodebuild.cpp b/src/nodebuild.cpp
index 9fa95d9cf..5ac860bef 100644
--- a/src/nodebuild.cpp
+++ b/src/nodebuild.cpp
@@ -65,8 +65,8 @@ const int AAPreference = 16;
 FNodeBuilder::FNodeBuilder(FLevel &level)
 : Level(level), GLNodes(false), SegsStuffed(0)
 {
-
 	VertexMap = NULL;
+	OldVertexTable = NULL;
 }
 
 FNodeBuilder::FNodeBuilder (FLevel &level,
@@ -84,10 +84,14 @@ FNodeBuilder::FNodeBuilder (FLevel &level,
 
 FNodeBuilder::~FNodeBuilder()
 {
-	if (VertexMap != 0)
+	if (VertexMap != NULL)
 	{
 		delete VertexMap;
 	}
+	if (OldVertexTable != NULL)
+	{
+		delete OldVertexTable;
+	}
 }
 
 void FNodeBuilder::BuildMini(bool makeGLNodes)
diff --git a/src/nodebuild.h b/src/nodebuild.h
index da82e26a2..a6f0459a0 100644
--- a/src/nodebuild.h
+++ b/src/nodebuild.h
@@ -209,6 +209,7 @@ public:
 		seg_t *&segs, glsegextra_t *&glsegextras, int &segCount,
 		subsector_t *&ssecs, int &subCount,
 		vertex_t *&verts, int &vertCount);
+	const int *GetOldVertexTable();
 
 	// These are used for building sub-BSP trees for polyobjects.
 	void Clear();
@@ -227,6 +228,7 @@ public:
 
 private:
 	IVertexMap *VertexMap;
+	int *OldVertexTable;
 
 	TArray<node_t> Nodes;
 	TArray<subsector_t> Subsectors;
diff --git a/src/nodebuild_utility.cpp b/src/nodebuild_utility.cpp
index ac4671075..b37533921 100644
--- a/src/nodebuild_utility.cpp
+++ b/src/nodebuild_utility.cpp
@@ -75,7 +75,7 @@ angle_t FNodeBuilder::PointToAngle (fixed_t x, fixed_t y)
 
 void FNodeBuilder::FindUsedVertices (vertex_t *oldverts, int max)
 {
-	int *map = (int *)alloca (max*sizeof(int));
+	int *map = new int[max];
 	int i;
 	FPrivVert newvert;
 
@@ -102,6 +102,17 @@ void FNodeBuilder::FindUsedVertices (vertex_t *oldverts, int max)
 		Level.Lines[i].v1 = (vertex_t *)(size_t)map[v1];
 		Level.Lines[i].v2 = (vertex_t *)(size_t)map[v2];
 	}
+	OldVertexTable = map;
+}
+
+// Retrieves the original vertex -> current vertex table.
+// Doing so prevents the node builder from freeing it.
+
+const int *FNodeBuilder::GetOldVertexTable()
+{
+	int *table = OldVertexTable;
+	OldVertexTable = NULL;
+	return table;
 }
 
 // For every sidedef in the map, create a corresponding seg.
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index 340b6df63..ce8a72da3 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -73,7 +73,7 @@
 
 #define MISSING_TEXTURE_WARN_LIMIT		20
 
-void P_SpawnSlopeMakers (FMapThing *firstmt, FMapThing *lastmt);
+void P_SpawnSlopeMakers (FMapThing *firstmt, FMapThing *lastmt, const int *oldvertextable);
 void P_SetSlopes ();
 void P_CopySlopes();
 void BloodCrypt (void *data, int key, int len);
@@ -3444,6 +3444,7 @@ void P_SetupLevel (char *lumpname, int position)
 	int numbuildthings;
 	int i;
 	bool buildmap;
+	const int *oldvertextable = NULL;
 
 	// This is motivated as follows:
 
@@ -3758,7 +3759,7 @@ void P_SetupLevel (char *lumpname, int position)
 	bool BuildGLNodes;
 	if (ForceNodeBuild)
 	{
-		BuildGLNodes = Renderer->RequireGLNodes() || am_textured || multiplayer || demoplayback || demorecording || genglnodes;
+		BuildGLNodes = RequireGLNodes || multiplayer || demoplayback || demorecording || genglnodes;
 
 		startTime = I_FPSTime ();
 		TArray<FNodeBuilder::FPolyStart> polyspots, anchors;
@@ -3782,6 +3783,7 @@ void P_SetupLevel (char *lumpname, int position)
 			vertexes, numvertexes);
 		endTime = I_FPSTime ();
 		DPrintf ("BSP generation took %.3f sec (%d segs)\n", (endTime - startTime) * 0.001, numsegs);
+		oldvertextable = builder.GetOldVertexTable();
 		reloop = true;
 	}
 	else
@@ -3868,7 +3870,7 @@ void P_SetupLevel (char *lumpname, int position)
 	if (!buildmap)
 	{
 		// [RH] Spawn slope creating things first.
-		P_SpawnSlopeMakers (&MapThingsConverted[0], &MapThingsConverted[MapThingsConverted.Size()]);
+		P_SpawnSlopeMakers (&MapThingsConverted[0], &MapThingsConverted[MapThingsConverted.Size()], oldvertextable);
 		P_CopySlopes();
 
 		// Spawn 3d floors - must be done before spawning things so it can't be done in P_SpawnSpecials
@@ -3898,6 +3900,10 @@ void P_SetupLevel (char *lumpname, int position)
 		delete[] buildthings;
 	}
 	delete map;
+	if (oldvertextable != NULL)
+	{
+		delete[] oldvertextable;
+	}
 
 	// set up world state
 	P_SpawnSpecials ();
diff --git a/src/p_slopes.cpp b/src/p_slopes.cpp
index 5ac7cf704..07ddf2e0d 100644
--- a/src/p_slopes.cpp
+++ b/src/p_slopes.cpp
@@ -280,7 +280,7 @@ enum
 //
 //==========================================================================
 
-static void P_SetSlopesFromVertexHeights(FMapThing *firstmt, FMapThing *lastmt)
+static void P_SetSlopesFromVertexHeights(FMapThing *firstmt, FMapThing *lastmt, const int *oldvertextable)
 {
 	TMap<int, fixed_t> vt_heights[2];
 	FMapThing *mt;
@@ -311,15 +311,17 @@ static void P_SetSlopesFromVertexHeights(FMapThing *firstmt, FMapThing *lastmt)
 
 	for(int i = 0; i < numvertexdatas; i++)
 	{
+		int ii = oldvertextable == NULL ? i : oldvertextable[i];
+
 		if (vertexdatas[i].flags & VERTEXFLAG_ZCeilingEnabled)
 		{
-			vt_heights[1][i] = vertexdatas[i].zCeiling;
+			vt_heights[1][ii] = vertexdatas[i].zCeiling;
 			vt_found = true;
 		}
 
 		if (vertexdatas[i].flags & VERTEXFLAG_ZFloorEnabled)
 		{
-			vt_heights[0][i] = vertexdatas[i].zFloor;
+			vt_heights[0][ii] = vertexdatas[i].zFloor;
 			vt_found = true;
 		}
 	}
@@ -413,7 +415,7 @@ static void P_SetSlopesFromVertexHeights(FMapThing *firstmt, FMapThing *lastmt)
 //
 //===========================================================================
 
-void P_SpawnSlopeMakers (FMapThing *firstmt, FMapThing *lastmt)
+void P_SpawnSlopeMakers (FMapThing *firstmt, FMapThing *lastmt, const int *oldvertextable)
 {
 	FMapThing *mt;
 
@@ -421,7 +423,7 @@ void P_SpawnSlopeMakers (FMapThing *firstmt, FMapThing *lastmt)
 	{
 		if ((mt->type >= THING_SlopeFloorPointLine &&
 			 mt->type <= THING_SetCeilingSlope) ||
-			mt->type==THING_VavoomFloor || mt->type==THING_VavoomCeiling)
+			mt->type == THING_VavoomFloor || mt->type == THING_VavoomCeiling)
 		{
 			fixed_t x, y, z;
 			secplane_t *refplane;
@@ -439,7 +441,7 @@ void P_SpawnSlopeMakers (FMapThing *firstmt, FMapThing *lastmt)
 				refplane = &sec->floorplane;
 			}
 			z = refplane->ZatPoint (x, y) + (mt->z);
-			if (mt->type==THING_VavoomFloor || mt->type==THING_VavoomCeiling)
+			if (mt->type == THING_VavoomFloor || mt->type == THING_VavoomCeiling)
 			{
 				P_VavoomSlope(sec, mt->thingid, x, y, mt->z, mt->type & 1); 
 			}
@@ -465,7 +467,7 @@ void P_SpawnSlopeMakers (FMapThing *firstmt, FMapThing *lastmt)
 		}
 	}
 
-	P_SetSlopesFromVertexHeights(firstmt, lastmt);
+	P_SetSlopesFromVertexHeights(firstmt, lastmt, oldvertextable);
 }