diff --git a/src/road_cmd.cpp b/src/road_cmd.cpp
--- a/src/road_cmd.cpp
+++ b/src/road_cmd.cpp
@@ -1337,7 +1337,7 @@ void UpdateNearestTownForRoadTiles(bool 
 	}
 }
 
-static uint GetSlopePixelZ_Road(TileIndex tile, uint x, uint y)
+static int GetSlopePixelZ_Road(TileIndex tile, uint x, uint y)
 {
 
 	if (IsNormalRoad(tile)) {
@@ -1677,7 +1677,7 @@ static void ChangeTileOwner_Road(TileInd
 	}
 }
 
-static CommandCost TerraformTile_Road(TileIndex tile, DoCommandFlag flags, uint z_new, Slope tileh_new)
+static CommandCost TerraformTile_Road(TileIndex tile, DoCommandFlag flags, int z_new, Slope tileh_new)
 {
 	if (_settings_game.construction.build_on_slopes && AutoslopeEnabled()) {
 		switch (GetRoadTileType(tile)) {