diff --git a/source/core/maptypes.h b/source/core/maptypes.h
index 52b937577..04f4b026d 100644
--- a/source/core/maptypes.h
+++ b/source/core/maptypes.h
@@ -296,6 +296,8 @@ struct walltype
 
 	FTextureID walltexture() const;
 	FTextureID overtexture() const;
+	void setwalltexture(FTextureID tex);
+	void setovertexture(FTextureID tex);
 };
 
 // enable for running a compile-check to ensure that renderer-critical variables are not being written to directly.
diff --git a/source/core/textures/buildtiles.cpp b/source/core/textures/buildtiles.cpp
index 4acef569e..2de9360a2 100644
--- a/source/core/textures/buildtiles.cpp
+++ b/source/core/textures/buildtiles.cpp
@@ -695,31 +695,26 @@ PicAnm picanm;
 // wrappers that allow partial migration to a textureID-based setup.
 FTextureID walltype::walltexture() const
 {
-	auto tex = tileGetTexture(wallpicnum);
-	return tex ? tex->GetID() : FNullTextureID();
+	return tileGetTextureID(wallpicnum);
 }
 FTextureID walltype::overtexture() const
 {
-	auto tex = tileGetTexture(overpicnum);
-	return tex ? tex->GetID() : FNullTextureID();
+	return tileGetTextureID(overpicnum);
 }
 
 const FTextureID sectortype::ceilingtexture() const
 {
-	auto tex = tileGetTexture(ceilingpicnum);
-	return tex ? tex->GetID() : FNullTextureID();
+	return tileGetTextureID(ceilingpicnum);
 }
 
 const FTextureID sectortype::floortexture() const
 {
-	auto tex = tileGetTexture(floorpicnum);
-	return tex ? tex->GetID() : FNullTextureID();
+	return tileGetTextureID(floorpicnum);
 }
 
 FTextureID spritetypebase::spritetexture() const
 {
-	auto tex = tileGetTexture(picnum);
-	return tex ? tex->GetID() : FNullTextureID();
+	return tileGetTextureID(picnum);
 }
 
 void sectortype::setfloortexture(FTextureID tex)
@@ -733,3 +728,16 @@ void sectortype::setceilingtexture(FTextureID tex)
 	auto p = TileFiles.textotile.CheckKey(tex.GetIndex());
 	if (p) ceilingpicnum = *p;
 }
+
+void walltype::setwalltexture(FTextureID tex)
+{
+	auto p = TileFiles.textotile.CheckKey(tex.GetIndex());
+	if (p) wallpicnum = *p; 
+}
+
+void walltype::setovertexture(FTextureID tex)
+{
+	auto p = TileFiles.textotile.CheckKey(tex.GetIndex());
+	if (p) overpicnum = *p;
+	else overpicnum = -1;	// unlike the others this one can be invalid.
+}
diff --git a/source/core/textures/buildtiles.h b/source/core/textures/buildtiles.h
index ee91e0d88..bfa7dd9bf 100644
--- a/source/core/textures/buildtiles.h
+++ b/source/core/textures/buildtiles.h
@@ -471,7 +471,7 @@ inline void tileUpdatePicnum(int* const tileptr, bool mayrotate = false, int ran
 
 inline FGameTexture* tileGetTexture(int tile, bool animate = false)
 {
-	assert((unsigned)tile < MAXTILES);
+	assert((unsigned)tile < MAXTILES && tile != -1);	// -1 is valid for overpicnum as 'no texture'.
 	if (tile < 0 || tile >= MAXTILES) return nullptr;
 	if (animate) tileUpdatePicnum(&tile);
 	return TileFiles.tiledata[tile].texture;
@@ -483,6 +483,12 @@ inline FTextureID tileGetTextureID(int tile)
 	return TileFiles.tiledata[tile].texture->GetID();
 }
 
+inline int legacyTileNum(FTextureID tex)
+{
+	auto p = TileFiles.textotile.CheckKey(tex.GetIndex());
+	return p ? *p : -1;
+}
+
 void tileUpdateAnimations();
 
 struct TileImport