diff --git a/lib/mbtiles.js b/lib/mbtiles.js
index a0b98d5..823ecbc 100644
--- a/lib/mbtiles.js
+++ b/lib/mbtiles.js
@@ -565,6 +565,7 @@ MBTiles.prototype.putTile = function(z, x, y, data, callback) {
 MBTiles.prototype.putGrid = function(z, x, y, data, callback) {
     if (typeof callback !== 'function') throw new Error('Callback needed');
     if (!this.open) return callback(new Error('MBTiles not yet loaded'));
+    if (!this._isWritable) return callback(new Error('MBTiles not in write mode'));
 
     // Flip Y coordinate because MBTiles files are TMS.
     y = (1 << z) - 1 - y;