diff --git a/src/gl/scene/gl_walls.cpp b/src/gl/scene/gl_walls.cpp
index 5db32de04..7b9d47c3f 100644
--- a/src/gl/scene/gl_walls.cpp
+++ b/src/gl/scene/gl_walls.cpp
@@ -1392,6 +1392,12 @@ void GLWall::DoFFloorBlocks(seg_t * seg, sector_t * frontsector, sector_t * back
 			ff_topleft = topleft;
 			ff_topright = topright;
 		}
+		if (ff_bottomleft < bottomleft && ff_bottomright < bottomright)
+		{
+			// the new section extends into the floor.
+			ff_bottomleft = bottomleft;
+			ff_bottomright = bottomright;
+		}
 
 		// do all inverse floors above the current one it there is a gap between the
 		// last 3D floor and this one.