diff --git a/src/p_maputl.c b/src/p_maputl.c
index 6ba8f1d59..111103294 100644
--- a/src/p_maputl.c
+++ b/src/p_maputl.c
@@ -720,7 +720,7 @@ void P_LineOpening(line_t *linedef, mobj_t *mobj)
 				delta1 = abs(mobj->z - (bottomheight + ((topheight - bottomheight)/2)));
 				delta2 = abs(thingtop - (bottomheight + ((topheight - bottomheight)/2)));
 
-				if (delta1 >= delta2 && !(rover->flags & FF_PLATFORM)) // thing is below FOF
+				if (delta1 >= delta2 && (rover->flags & FF_INTANGABLEFLATS) != FF_PLATFORM) // thing is below FOF
 				{
 					if (bottomheight < opentop) {
 						opentop = bottomheight;
@@ -733,7 +733,7 @@ void P_LineOpening(line_t *linedef, mobj_t *mobj)
 						highceiling = bottomheight;
 				}
 
-				if (delta1 < delta2 && !(rover->flags & FF_REVERSEPLATFORM)) // thing is above FOF
+				if (delta1 < delta2 && (rover->flags & FF_INTANGABLEFLATS) != FF_REVERSEPLATFORM) // thing is above FOF
 				{
 					if (topheight > openbottom) {
 						openbottom = topheight;