diff --git a/src/object_cmd.cpp b/src/object_cmd.cpp
index 2bb29628f9..ae74e5e5cf 100644
--- a/src/object_cmd.cpp
+++ b/src/object_cmd.cpp
@@ -769,11 +769,14 @@ static bool TryBuildLightHouse()
 	}
 
 	/* Only build lighthouses at tiles where the border is sea. */
-	if (!IsTileType(tile, MP_WATER)) return false;
+	if (!IsTileType(tile, MP_WATER) || GetWaterClass(tile) != WATER_CLASS_SEA) return false;
 
 	for (int j = 0; j < 19; j++) {
 		int h;
 		if (IsTileType(tile, MP_CLEAR) && IsTileFlat(tile, &h) && h <= 2 && !IsBridgeAbove(tile)) {
+			for (auto t : SpiralTileSequence(tile, 9)) {
+				if (IsObjectTypeTile(t, OBJECT_LIGHTHOUSE)) return false;
+			}
 			BuildObject(OBJECT_LIGHTHOUSE, tile);
 			assert(tile < Map::Size());
 			return true;