diff --git a/lib/mbtiles.js b/lib/mbtiles.js
index d821488..9b77a0e 100644
--- a/lib/mbtiles.js
+++ b/lib/mbtiles.js
@@ -566,7 +566,7 @@ MBTiles.prototype.putGrid = function(z, x, y, data, callback) {
 
     // Preprocess grid data.
     var json = JSON.stringify({ grid: data.grid, keys: data.keys });
-    var id = crypto.createHash('md5').update(json).digest('hex');
+    var id = data.id || crypto.createHash('md5').update(json).digest('hex');
     if (!this._gridCache[id]) {
         // This corresponds to the grid_utfgrid table.
         this._gridCache[id] = zlib.deflate(new Buffer(json, 'utf8'));