diff --git a/src/p_user.c b/src/p_user.c
index 921f1240..f2f0cb77 100644
--- a/src/p_user.c
+++ b/src/p_user.c
@@ -1940,6 +1940,7 @@ static void P_CheckQuicksand(player_t *player)
 {
 	ffloor_t *rover;
 	fixed_t sinkspeed, friction;
+	fixed_t topheight, bottomheight;
 
 	if (!(player->mo->subsector->sector->ffloors && player->mo->momz <= 0))
 		return;
@@ -1951,16 +1952,33 @@ static void P_CheckQuicksand(player_t *player)
 		if (!(rover->flags & FF_QUICKSAND))
 			continue;
 
-		if (*rover->topheight >= player->mo->z && *rover->bottomheight < player->mo->z + player->mo->height)
+		topheight = P_GetSpecialTopZ(player->mo, sectors + rover->secnum, player->mo->subsector->sector);
+		bottomheight = P_GetSpecialBottomZ(player->mo, sectors + rover->secnum, player->mo->subsector->sector);
+
+		if (topheight >= player->mo->z && bottomheight < player->mo->z + player->mo->height)
 		{
 			sinkspeed = abs(rover->master->v1->x - rover->master->v2->x)>>1;
 
 			sinkspeed = FixedDiv(sinkspeed,TICRATE*FRACUNIT);
 
-			player->mo->z -= sinkspeed;
+			if (player->mo->eflags & MFE_VERTICALFLIP)
+			{
+				fixed_t ceilingheight = P_GetCeilingZ(player->mo, player->mo->subsector->sector, player->mo->x, player->mo->y, NULL);
 
-			if (player->mo->z <= player->mo->subsector->sector->floorheight)
-				player->mo->z = player->mo->subsector->sector->floorheight;
+				player->mo->z += sinkspeed;
+
+				if (player->mo->z + player->mo->height >= ceilingheight)
+					player->mo->z = ceilingheight - player->mo->height;
+			}
+			else
+			{
+				fixed_t floorheight = P_GetFloorZ(player->mo, player->mo->subsector->sector, player->mo->x, player->mo->y, NULL);
+
+				player->mo->z -= sinkspeed;
+
+				if (player->mo->z <= floorheight)
+					player->mo->z = floorheight;
+			}
 
 			friction = abs(rover->master->v1->y - rover->master->v2->y)>>6;