diff --git a/src/p_mobj.c b/src/p_mobj.c
index 03e7e9f99..96651dd74 100644
--- a/src/p_mobj.c
+++ b/src/p_mobj.c
@@ -578,6 +578,8 @@ static fixed_t HighestOnLine(fixed_t radius, fixed_t x, fixed_t y, line_t *line,
 		);
 }
 
+#define NOCOLLISION ((mobj->flags & MF_NOBLOCKMAP) || (mobj->flags & MF_NOCLIPTHING))
+
 fixed_t P_MobjFloorZ(mobj_t *mobj, sector_t *sector, sector_t *boundsec, fixed_t x, fixed_t y, line_t *line, boolean lowest, boolean perfect)
 {
 	I_Assert(mobj != NULL);
@@ -608,7 +610,7 @@ fixed_t P_MobjFloorZ(mobj_t *mobj, sector_t *sector, sector_t *boundsec, fixed_t
 		testy += y;
 
 		// If the highest point is in the sector, then we have it easy! Just get the Z at that point
-		if (R_PointInSubsector(testx, testy)->sector == (boundsec ? boundsec : sector))
+		if (NOCOLLISION ? R_IsPointInSector(boundsec ? boundsec : sector, testx, testy) : R_PointInSubsector(testx, testy)->sector == (boundsec ? boundsec : sector))
 			return P_GetZAt(slope, testx, testy);
 
 		// If boundsec is set, we're looking for specials. In that case, iterate over every line in this sector to find the TRUE highest/lowest point
@@ -685,7 +687,7 @@ fixed_t P_MobjCeilingZ(mobj_t *mobj, sector_t *sector, sector_t *boundsec, fixed
 		testy += y;
 
 		// If the highest point is in the sector, then we have it easy! Just get the Z at that point
-		if (R_PointInSubsector(testx, testy)->sector == (boundsec ? boundsec : sector))
+		if (NOCOLLISION ? R_IsPointInSector(boundsec ? boundsec : sector, testx, testy) : R_PointInSubsector(testx, testy)->sector == (boundsec ? boundsec : sector))
 			return P_GetZAt(slope, testx, testy);
 
 		// If boundsec is set, we're looking for specials. In that case, iterate over every line in this sector to find the TRUE highest/lowest point
@@ -764,7 +766,7 @@ fixed_t P_CameraFloorZ(camera_t *mobj, sector_t *sector, sector_t *boundsec, fix
 		testy += y;
 
 		// If the highest point is in the sector, then we have it easy! Just get the Z at that point
-		if (R_PointInSubsector(testx, testy)->sector == (boundsec ? boundsec : sector))
+		if (R_IsPointInSector(boundsec ? boundsec : sector, testx, testy))
 			return P_GetZAt(slope, testx, testy);
 
 		// If boundsec is set, we're looking for specials. In that case, iterate over every line in this sector to find the TRUE highest/lowest point
@@ -842,7 +844,7 @@ fixed_t P_CameraCeilingZ(camera_t *mobj, sector_t *sector, sector_t *boundsec, f
 		testy += y;
 
 		// If the highest point is in the sector, then we have it easy! Just get the Z at that point
-		if (R_PointInSubsector(testx, testy)->sector == (boundsec ? boundsec : sector))
+		if (R_IsPointInSector(boundsec ? boundsec : sector, testx, testy))
 			return P_GetZAt(slope, testx, testy);
 
 		// If boundsec is set, we're looking for specials. In that case, iterate over every line in this sector to find the TRUE highest/lowest point
diff --git a/src/r_main.c b/src/r_main.c
index 9541fef41..6dbd8f059 100644
--- a/src/r_main.c
+++ b/src/r_main.c
@@ -1026,6 +1026,50 @@ void R_Init(void)
 	framecount = 0;
 }
 
+//
+// R_IsPointInSector
+//
+boolean R_IsPointInSector(sector_t *sector, fixed_t x, fixed_t y)
+{
+	size_t i;
+	size_t passes = 0;
+
+	for (i = 0; i < sector->linecount; i++)
+	{
+		line_t *line = sector->lines[i];
+		vertex_t *v1, *v2;
+
+		if (line->frontsector == line->backsector)
+			continue;
+
+		v1 = line->v1;
+		v2 = line->v2;
+
+		// make sure v1 is below v2
+		if (v1->y > v2->y)
+		{
+			vertex_t *tmp = v1;
+			v1 = v2;
+			v2 = tmp;
+		}
+		else if (v1->y == v2->y) // horizontal line, we can't match this
+			continue;
+
+		if (v1->y < y && y <= v2->y)
+		{
+			// if the y axis in inside the line, find the point where we intersect on the x axis...
+			fixed_t vx = v1->x + (INT64)(v2->x - v1->x) * (y - v1->y) / (v2->y - v1->y);
+
+			// ...and if that point is to the left of the point, count it as inside.
+			if (vx < x)
+				passes++;
+		}
+	}
+
+	// and odd number of passes means we're inside the polygon.
+	return passes % 2;
+}
+
 //
 // R_IsPointInSubsector, same as above but returns 0 if not in subsector
 //
diff --git a/src/r_main.h b/src/r_main.h
index 523e924d5..3fbc3dd99 100644
--- a/src/r_main.h
+++ b/src/r_main.h
@@ -125,6 +125,7 @@ angle_t R_PlayerSliptideAngle(player_t *player);
 
 fixed_t R_ScaleFromGlobalAngle(angle_t visangle);
 
+boolean R_IsPointInSector(sector_t *sector, fixed_t x, fixed_t y);
 subsector_t *R_IsPointInSubsector(fixed_t x, fixed_t y);
 
 //