diff --git a/src/p_map.cpp b/src/p_map.cpp
index 9f8cc6271..92b2cb035 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -149,7 +149,7 @@ static bool PIT_FindFloorCeiling (line_t *ld, const FBoundingBox &box, FCheckPos
 	if (open.bottom > tmf.floorz)
 	{
 		tmf.floorz = open.bottom;
-		tmf.floorsector = open.bottomsec;
+		if (open.bottomsec != NULL) tmf.floorsector = open.bottomsec;
 		tmf.touchmidtex = open.touchmidtex;
 		tmf.abovemidtex = open.abovemidtex;
 	}