diff --git a/tslib.es6.js b/tslib.es6.js
index d2ce81c..2a5c518 100644
--- a/tslib.es6.js
+++ b/tslib.es6.js
@@ -108,14 +108,15 @@ export function __exportStar(m, exports) {
 }
 
 export function __values(o) {
-    var m = typeof Symbol === "function" && o[Symbol.iterator], i = 0;
+    var s = typeof Symbol === "function" && Symbol.iterator, m = s && o[s], i = 0;
     if (m) return m.call(o);
-    return {
+    if (o && typeof o.length === "number") return {
         next: function () {
             if (o && i >= o.length) o = void 0;
             return { value: o && o[i++], done: !o };
         }
     };
+    throw new TypeError(s ? "Object not iterable." : "Symbol.iterator is not defined.");
 }
 
 export function __read(o, n) {
diff --git a/tslib.js b/tslib.js
index 303bc52..7034196 100644
--- a/tslib.js
+++ b/tslib.js
@@ -145,14 +145,15 @@ var __importDefault;
     };
 
     __values = function (o) {
-        var m = typeof Symbol === "function" && o[Symbol.iterator], i = 0;
+        var s = typeof Symbol === "function" && Symbol.iterator, m = s && o[s], i = 0;
         if (m) return m.call(o);
-        return {
+        if (o && typeof o.length === "number") return {
             next: function () {
                 if (o && i >= o.length) o = void 0;
                 return { value: o && o[i++], done: !o };
             }
         };
+        throw new TypeError(s ? "Object not iterable." : "Symbol.iterator is not defined.");
     };
 
     __read = function (o, n) {