diff --git a/src/gl/scene/gl_walls.cpp b/src/gl/scene/gl_walls.cpp
index c59d4a041..231503407 100644
--- a/src/gl/scene/gl_walls.cpp
+++ b/src/gl/scene/gl_walls.cpp
@@ -1588,7 +1588,7 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 			}
 			else if (!(seg->sidedef->Flags & WALLF_POLYOBJ))
 			{
-				if ((frontsector->ceilingplane.isSlope() || backsector->ceilingplane.isSlope()) &&
+				if ((frontsector->floorplane.isSlope() || backsector->floorplane.isSlope()) &&
 					frontsector->GetTexture(sector_t::floor) != skyflatnum &&
 					backsector->GetTexture(sector_t::floor) != skyflatnum)
 				{