diff --git a/tslib.es6.js b/tslib.es6.js
index 5055a74..d2ce81c 100644
--- a/tslib.es6.js
+++ b/tslib.es6.js
@@ -66,10 +66,11 @@ export function __metadata(metadataKey, metadataValue) {
 }
 
 export function __awaiter(thisArg, _arguments, P, generator) {
+    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
     return new (P || (P = Promise))(function (resolve, reject) {
         function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
         function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
-        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
+        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
         step((generator = generator.apply(thisArg, _arguments || [])).next());
     });
 }
diff --git a/tslib.js b/tslib.js
index 34615c1..303bc52 100644
--- a/tslib.js
+++ b/tslib.js
@@ -103,10 +103,11 @@ var __importDefault;
     };
 
     __awaiter = function (thisArg, _arguments, P, generator) {
+        function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
         return new (P || (P = Promise))(function (resolve, reject) {
             function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
             function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
-            function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
+            function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
             step((generator = generator.apply(thisArg, _arguments || [])).next());
         });
     };