diff --git a/util.js b/util.js
index 3039e34..a29f3d0 100644
--- a/util.js
+++ b/util.js
@@ -162,7 +162,7 @@ var build_array_query = function(data, prefix)
 		if (typeof data[i] == 'object')
 			s += build_array_query(data[i], k);
 		else
-			s = s+'&'+k+'='+(data[i] === false || data[i] === null ? '' : encodeURIComponent(data[i]));
+			s = s+'&'+k+'='+(data[i] === false || data[i] === null || data[i] === undefined ? '' : encodeURIComponent(data[i]));
 	}
 	return s;
 };