diff --git a/src/p_mobj.c b/src/p_mobj.c
index f12e73ad8..9432d5625 100644
--- a/src/p_mobj.c
+++ b/src/p_mobj.c
@@ -3039,8 +3039,8 @@ void P_MobjCheckWater(mobj_t *mobj)
 	{
 		fixed_t topheight, bottomheight;
 
-		topheight    = P_GetFFloorTopZAt   (rover, mobj->x, mobj->y);
-		bottomheight = P_GetFFloorBottomZAt(rover, mobj->x, mobj->y);
+		topheight = P_GetSpecialTopZ(mobj, sectors + rover->secnum, sector);
+		bottomheight = P_GetSpecialBottomZ(mobj, sectors + rover->secnum, sector);
 
 		if (!(rover->flags & FF_EXISTS) || !(rover->flags & FF_SWIMMABLE)
 		 || (((rover->flags & FF_BLOCKPLAYER) && mobj->player)