diff --git a/src/rendering/hwrenderer/doom_levelmesh.cpp b/src/rendering/hwrenderer/doom_levelmesh.cpp
index 6ec534fa4b..77e22471ca 100644
--- a/src/rendering/hwrenderer/doom_levelmesh.cpp
+++ b/src/rendering/hwrenderer/doom_levelmesh.cpp
@@ -154,6 +154,7 @@ void DoomLevelMesh::CreateSideSurfaces(FLevelLocals &doomMap, side_t *side)
 			surf.type = ST_MIDDLEWALL;
 			surf.typeIndex = typeIndex;
 			surf.controlSector = xfloor->model;
+			surf.bSky = false;
 
 			FVector3 verts[4];
 			verts[0].X = verts[2].X = v2.X;
@@ -213,6 +214,7 @@ void DoomLevelMesh::CreateSideSurfaces(FLevelLocals &doomMap, side_t *side)
 				surf.plane = ToPlane(verts[0], verts[1], verts[2]);
 				surf.type = ST_LOWERWALL;
 				surf.typeIndex = typeIndex;
+				surf.bSky = false;
 				surf.controlSector = nullptr;
 
 				Surfaces.Push(surf);
@@ -265,6 +267,7 @@ void DoomLevelMesh::CreateSideSurfaces(FLevelLocals &doomMap, side_t *side)
 	if (back == nullptr)
 	{
 		Surface surf;
+		surf.bSky = false;
 
 		FVector3 verts[4];
 		verts[0].X = verts[2].X = v1.X;
@@ -278,6 +281,7 @@ void DoomLevelMesh::CreateSideSurfaces(FLevelLocals &doomMap, side_t *side)
 
 		surf.startVertIndex = MeshVertices.Size();
 		surf.numVerts = 4;
+		surf.bSky = false;
 		MeshVertices.Push(verts[0]);
 		MeshVertices.Push(verts[1]);
 		MeshVertices.Push(verts[2]);
@@ -295,6 +299,7 @@ void DoomLevelMesh::CreateSideSurfaces(FLevelLocals &doomMap, side_t *side)
 void DoomLevelMesh::CreateFloorSurface(FLevelLocals &doomMap, subsector_t *sub, sector_t *sector, int typeIndex, bool is3DFloor)
 {
 	Surface surf;
+	surf.bSky = IsSkySector(sector, sector_t::floor);
 
 	if (!is3DFloor)
 	{
@@ -331,7 +336,7 @@ void DoomLevelMesh::CreateFloorSurface(FLevelLocals &doomMap, subsector_t *sub,
 void DoomLevelMesh::CreateCeilingSurface(FLevelLocals &doomMap, subsector_t *sub, sector_t *sector, int typeIndex, bool is3DFloor)
 {
 	Surface surf;
-	surf.bSky = IsSkySector(sector);
+	surf.bSky = IsSkySector(sector, sector_t::ceiling);
 
 	if (!is3DFloor)
 	{
@@ -393,7 +398,7 @@ void DoomLevelMesh::CreateSubsectorSurfaces(FLevelLocals &doomMap)
 
 bool DoomLevelMesh::IsTopSideSky(sector_t* frontsector, sector_t* backsector, side_t* side)
 {
-	return IsSkySector(frontsector) && IsSkySector(backsector);
+	return IsSkySector(frontsector, sector_t::ceiling) && IsSkySector(backsector, sector_t::ceiling);
 }
 
 bool DoomLevelMesh::IsTopSideVisible(side_t* side)
@@ -408,9 +413,10 @@ bool DoomLevelMesh::IsBottomSideVisible(side_t* side)
 	return tex && tex->isValid();
 }
 
-bool DoomLevelMesh::IsSkySector(sector_t* sector)
+bool DoomLevelMesh::IsSkySector(sector_t* sector, int plane)
 {
-	return sector->GetTexture(sector_t::ceiling) == skyflatnum;
+	// plane is either sector_t::ceiling or sector_t::floor
+	return sector->GetTexture(plane) == skyflatnum;
 }
 
 bool DoomLevelMesh::IsControlSector(sector_t* sector)
diff --git a/src/rendering/hwrenderer/doom_levelmesh.h b/src/rendering/hwrenderer/doom_levelmesh.h
index bc8505d4fa..2d2aee75cf 100644
--- a/src/rendering/hwrenderer/doom_levelmesh.h
+++ b/src/rendering/hwrenderer/doom_levelmesh.h
@@ -49,7 +49,7 @@ private:
 	static bool IsTopSideSky(sector_t* frontsector, sector_t* backsector, side_t* side);
 	static bool IsTopSideVisible(side_t* side);
 	static bool IsBottomSideVisible(side_t* side);
-	static bool IsSkySector(sector_t* sector);
+	static bool IsSkySector(sector_t* sector, int plane);
 	static bool IsControlSector(sector_t* sector);
 
 	static secplane_t ToPlane(const FVector3& pt1, const FVector3& pt2, const FVector3& pt3)