diff --git a/tslib.es6.js b/tslib.es6.js
index 422345d..6905dff 100644
--- a/tslib.es6.js
+++ b/tslib.es6.js
@@ -185,11 +185,23 @@ export function __makeTemplateObject(cooked, raw) {
     return cooked;
 };
 
+var __getImportStarCache = function () {
+    if (typeof WeakMap !== "function") return null;
+
+    var cache = new WeakMap();
+    __getImportStarCache = function () { return cache; }
+    return cache;
+};
+
 export function __importStar(mod) {
     if (mod && mod.__esModule) return mod;
+    if (mod === null || (typeof mod !== "object" && typeof mod !== "function")) return { default: mod }
+    var cache = __getImportStarCache();
+    if (cache && cache.has(mod)) return cache.get(mod);
     var result = {};
-    if (mod != null) for (var k in mod) if (Object.hasOwnProperty.call(mod, k)) result[k] = mod[k];
+    for (var k in mod) if (Object.hasOwnProperty.call(mod, k)) result[k] = mod[k];
     result.default = mod;
+    if (cache) cache.set(mod, result);
     return result;
 }
 
diff --git a/tslib.js b/tslib.js
index f736d07..93136ab 100644
--- a/tslib.js
+++ b/tslib.js
@@ -222,11 +222,23 @@ var __importDefault;
         return cooked;
     };
 
+    var __getImportStarCache = function () {
+        if (typeof WeakMap !== "function") return null;
+
+        var cache = new WeakMap();
+        __getImportStarCache = function () { return cache; }
+        return cache;
+    };
+
     __importStar = function (mod) {
         if (mod && mod.__esModule) return mod;
+        if (mod === null || (typeof mod !== "object" && typeof mod !== "function")) return { "default": mod }
+        var cache = __getImportStarCache();
+        if (cache && cache.has(mod)) return cache.get(mod);
         var result = {};
-        if (mod != null) for (var k in mod) if (Object.hasOwnProperty.call(mod, k)) result[k] = mod[k];
+        for (var k in mod) if (Object.hasOwnProperty.call(mod, k)) result[k] = mod[k];
         result["default"] = mod;
+        if (cache) cache.set(mod, result);
         return result;
     };