diff --git a/src/r_things.c b/src/r_things.c
index accd1e2b3..423276a59 100644
--- a/src/r_things.c
+++ b/src/r_things.c
@@ -3001,13 +3001,25 @@ void R_ClipVisSprite(vissprite_t *spr, INT32 x1, INT32 x2, drawseg_t* dsstart, p
 
 	if (portal)
 	{
-		for (x = x1; x <= x2; x++)
+		INT32 start_index = max(portal->start, x1);
+		INT32 end_index = min(portal->start + portal->end - portal->start, x2);
+		for (x = x1; x < start_index; x++)
+		{
+			spr->clipbot[x] = -1;
+			spr->cliptop[x] = -1;
+		}
+		for (x = start_index; x <= end_index; x++)
 		{
 			if (spr->clipbot[x] > portal->floorclip[x - portal->start])
 				spr->clipbot[x] = portal->floorclip[x - portal->start];
 			if (spr->cliptop[x] < portal->ceilingclip[x - portal->start])
 				spr->cliptop[x] = portal->ceilingclip[x - portal->start];
 		}
+		for (x = end_index + 1; x <= x2; x++)
+		{
+			spr->clipbot[x] = -1;
+			spr->cliptop[x] = -1;
+		}
 	}
 }