diff --git a/src/clear_cmd.cpp b/src/clear_cmd.cpp
--- a/src/clear_cmd.cpp
+++ b/src/clear_cmd.cpp
@@ -231,7 +231,7 @@ static void TileLoop_Clear(TileIndex til
 	/* If the tile is at any edge flood it to prevent maps without water. */
 	if (_settings_game.construction.freeform_edges && DistanceFromEdge(tile) == 1) {
 		uint z;
-		Slope slope = GetTilePixelSlope(tile, &z);
+		Slope slope = GetTileSlope(tile, &z);
 		if (z == 0 && slope == SLOPE_FLAT) {
 			DoFloodTile(tile);
 			MarkTileDirtyByTile(tile);