diff --git a/src/water_cmd.cpp b/src/water_cmd.cpp
index 6b4f41eb98..ccda7fb063 100644
--- a/src/water_cmd.cpp
+++ b/src/water_cmd.cpp
@@ -606,6 +606,8 @@ static bool IsWateredTile(TileIndex tile, Direction from)
 
 		case MP_TUNNELBRIDGE: return GetTunnelBridgeTransportType(tile) == TRANSPORT_WATER && ReverseDiagDir(GetTunnelBridgeDirection(tile)) == DirToDiagDir(from);
 
+		case MP_VOID: return true; // consider map border as water, esp. for rivers
+
 		default:          return false;
 	}
 }