diff --git a/src/r_things.c b/src/r_things.c
index 6130815e7..c31d295a8 100644
--- a/src/r_things.c
+++ b/src/r_things.c
@@ -1152,14 +1152,17 @@ fixed_t R_GetShadowZ(
 	mobj_t *thing, pslope_t **shadowslope,
 	fixed_t interpx, fixed_t interpy, fixed_t interpz)
 {
+	fixed_t halfHeight = interpz + (thing->height >> 1);
 	boolean isflipped = thing->eflags & MFE_VERTICALFLIP;
+	fixed_t floorz = P_GetFloorZ(thing, thing->subsector->sector, interpx, interpy, NULL);
+	fixed_t ceilingz = P_GetCeilingZ(thing, thing->subsector->sector, interpx, interpy, NULL);
 	fixed_t z, groundz = isflipped ? INT32_MAX : INT32_MIN;
 	pslope_t *slope, *groundslope = NULL;
 	msecnode_t *node;
 	sector_t *sector;
 	ffloor_t *rover;
 
-#define CHECKZ (isflipped ? z > interpz+thing->height/2 && z < groundz : z < interpz+thing->height/2 && z > groundz)
+#define CHECKZ (isflipped ? z > halfHeight && z < groundz : z < halfHeight && z > groundz)
 
 	for (node = thing->touching_sectorlist; node; node = node->m_sectorlist_next)
 	{
@@ -1194,10 +1197,10 @@ fixed_t R_GetShadowZ(
 			}
 	}
 
-	if (isflipped ? (thing->ceilingz < groundz - (!groundslope ? 0 : FixedMul(abs(groundslope->zdelta), thing->radius*3/2)))
-		: (thing->floorz > groundz + (!groundslope ? 0 : FixedMul(abs(groundslope->zdelta), thing->radius*3/2))))
+	if (isflipped ? (ceilingz < groundz - (!groundslope ? 0 : FixedMul(abs(groundslope->zdelta), thing->radius*3/2)))
+		: (floorz > groundz + (!groundslope ? 0 : FixedMul(abs(groundslope->zdelta), thing->radius*3/2))))
 	{
-		groundz = isflipped ? thing->ceilingz : thing->floorz;
+		groundz = isflipped ? ceilingz : floorz;
 		groundslope = NULL;
 	}
 
@@ -1208,10 +1211,10 @@ fixed_t R_GetShadowZ(
 	{
 		INT32 xl, xh, yl, yh, bx, by;
 
-		xl = (unsigned)(thing->x - thing->radius - bmaporgx)>>MAPBLOCKSHIFT;
-		xh = (unsigned)(thing->x + thing->radius - bmaporgx)>>MAPBLOCKSHIFT;
-		yl = (unsigned)(thing->y - thing->radius - bmaporgy)>>MAPBLOCKSHIFT;
-		yh = (unsigned)(thing->y + thing->radius - bmaporgy)>>MAPBLOCKSHIFT;
+		xl = (unsigned)(interpx - thing->radius - bmaporgx)>>MAPBLOCKSHIFT;
+		xh = (unsigned)(interpx + thing->radius - bmaporgx)>>MAPBLOCKSHIFT;
+		yl = (unsigned)(interpy - thing->radius - bmaporgy)>>MAPBLOCKSHIFT;
+		yh = (unsigned)(interpy + thing->radius - bmaporgy)>>MAPBLOCKSHIFT;
 
 		BMBOUNDFIX(xl, xh, yl, yh);
 
@@ -1248,7 +1251,7 @@ fixed_t R_GetShadowZ(
 						// We're inside it! Yess...
 						z = po->lines[0]->backsector->ceilingheight;
 
-						if (z < thing->z+thing->height/2 && z > groundz)
+						if (z < halfHeight && z > groundz)
 						{
 							groundz = z;
 							groundslope = NULL;