diff --git a/src/newgrf_canal.cpp b/src/newgrf_canal.cpp
--- a/src/newgrf_canal.cpp
+++ b/src/newgrf_canal.cpp
@@ -58,7 +58,7 @@ static uint32 CanalGetVariable(const Res
 		case 0x81: return GetTerrainType(tile);
 
 		/* Random data for river or canal tiles, otherwise zero */
-		case 0x83: return GetWaterTileRandomBits(tile);
+		case 0x83: return IsTileType(tile, MP_WATER) ? GetWaterTileRandomBits(tile) : 0;
 	}
 
 	DEBUG(grf, 1, "Unhandled canal variable 0x%02X", variable);