diff --git a/src/landscape.cpp b/src/landscape.cpp
index 544a41876b..2f534d3194 100644
--- a/src/landscape.cpp
+++ b/src/landscape.cpp
@@ -992,7 +992,7 @@ static void CreateDesertOrRainForest(uint desert_tropic_line)
  */
 static bool FindSpring(TileIndex tile, void *)
 {
-	int reference_height;
+	uint reference_height;
 	if (!IsTileFlat(tile, &reference_height) || IsWaterTile(tile)) return false;
 
 	/* In the tropics rivers start in the rainforest. */
diff --git a/src/object_cmd.cpp b/src/object_cmd.cpp
index d4f28477b9..0eb06a8702 100644
--- a/src/object_cmd.cpp
+++ b/src/object_cmd.cpp
@@ -783,7 +783,7 @@ static bool TryBuildLightHouse()
 	if (!IsTileType(tile, MP_WATER)) return false;
 
 	for (int j = 0; j < 19; j++) {
-		int h;
+		uint h;
 		if (IsTileType(tile, MP_CLEAR) && IsTileFlat(tile, &h) && h <= 2 && !IsBridgeAbove(tile)) {
 			BuildObject(OBJECT_LIGHTHOUSE, tile);
 			assert(tile < Map::Size());
@@ -802,7 +802,7 @@ static bool TryBuildLightHouse()
 static bool TryBuildTransmitter()
 {
 	TileIndex tile = RandomTile();
-	int h;
+	uint h;
 	if (IsTileType(tile, MP_CLEAR) && IsTileFlat(tile, &h) && h >= 4 && !IsBridgeAbove(tile)) {
 		TileIndex t = tile;
 		if (CircularTileSearch(&t, 9, HasTransmitter, nullptr)) return false;
diff --git a/src/tile_map.cpp b/src/tile_map.cpp
index 54cfc8ebd2..63bdc4d851 100644
--- a/src/tile_map.cpp
+++ b/src/tile_map.cpp
@@ -92,7 +92,7 @@ std::tuple<Slope, int> GetTilePixelSlopeOutsideMap(int x, int y)
  * @param h If not \c nullptr, pointer to storage of z height (only if tile is flat)
  * @return Whether the tile is flat
  */
-bool IsTileFlat(TileIndex tile, int *h)
+bool IsTileFlat(TileIndex tile, uint *h)
 {
 	uint x1 = TileX(tile);
 	uint y1 = TileY(tile);
diff --git a/src/tile_map.h b/src/tile_map.h
index 6fbb3a53fa..fb39822d22 100644
--- a/src/tile_map.h
+++ b/src/tile_map.h
@@ -269,7 +269,7 @@ std::tuple<Slope, int> GetTileSlopeZ(TileIndex tile);
 int GetTileZ(TileIndex tile);
 int GetTileMaxZ(TileIndex tile);
 
-bool IsTileFlat(TileIndex tile, int *h = nullptr);
+bool IsTileFlat(TileIndex tile, uint *h = nullptr);
 
 /**
  * Return the slope of a given tile inside the map.