diff --git a/lib/encoding.js b/lib/encoding.js
index 15e34b4..7a04bf8 100644
--- a/lib/encoding.js
+++ b/lib/encoding.js
@@ -1273,7 +1273,7 @@ if (typeof module !== "undefined" && module.exports) {
   /**
    * @param {string=} opt_string The string to encode.
    * @param {Object=} options
-   * @return {Uint8Array} Encoded bytes, as a Uint8Array.
+   * @return {!Uint8Array} Encoded bytes, as a Uint8Array.
    */
   TextEncoder.prototype.encode = function encode(opt_string, options) {
     opt_string = opt_string ? String(opt_string) : '';