diff --git a/main_gui.c b/main_gui.c
index cac653495f..c3c8277ad5 100644
--- a/main_gui.c
+++ b/main_gui.c
@@ -1200,11 +1200,9 @@ static void PlaceProc_RockyArea(TileIndex tile)
 
 static void PlaceProc_LightHouse(TileIndex tile)
 {
-	TileInfo ti;
-
-	FindLandscapeHeightByTile(&ti, tile);
-	if (!IsTileType(tile, MP_CLEAR) || IsSteepTileh(ti.tileh))
+	if (!IsTileType(tile, MP_CLEAR) || IsSteepTileh(GetTileSlope(tile, NULL))) {
 		return;
+	}
 
 	ModifyTile(tile, MP_SETTYPE(MP_UNMOVABLE) | MP_MAP5, 1);
 	SndPlayTileFx(SND_1F_SPLAT, tile);
@@ -1212,11 +1210,9 @@ static void PlaceProc_LightHouse(TileIndex tile)
 
 static void PlaceProc_Transmitter(TileIndex tile)
 {
-	TileInfo ti;
-
-	FindLandscapeHeightByTile(&ti, tile);
-	if (!IsTileType(tile, MP_CLEAR) || IsSteepTileh(ti.tileh))
+	if (!IsTileType(tile, MP_CLEAR) || IsSteepTileh(GetTileSlope(tile, NULL))) {
 		return;
+	}
 
 	ModifyTile(tile, MP_SETTYPE(MP_UNMOVABLE) | MP_MAP5, 0);
 	SndPlayTileFx(SND_1F_SPLAT, tile);
diff --git a/water_cmd.c b/water_cmd.c
index 3a5c3924ed..fcfa4211ba 100644
--- a/water_cmd.c
+++ b/water_cmd.c
@@ -39,9 +39,10 @@ static void FloodVehicle(Vehicle *v);
 
 static bool IsClearWaterTile(TileIndex tile)
 {
-	TileInfo ti;
-	FindLandscapeHeightByTile(&ti, tile);
-	return (ti.type == MP_WATER && ti.tileh == 0 && ti.map5 == 0);
+	return
+		IsTileType(tile, MP_WATER) &&
+		_m[tile].m5 == 0 &&
+		GetTileSlope(tile, NULL) == 0;
 }
 
 /** Build a ship depot.