diff --git a/modules/@angular/core/src/util/lang.ts b/modules/@angular/core/src/util/lang.ts
index 314473971c..6cf4316a83 100644
--- a/modules/@angular/core/src/util/lang.ts
+++ b/modules/@angular/core/src/util/lang.ts
@@ -6,6 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+/**
+ * Determine if the argument is shaped like a Promise
+ */
 export function isPromise(obj: any): obj is Promise<any> {
   // allow any Promise/A+ compliant thenable.
   // It's up to the caller to ensure that obj.then conforms to the spec
diff --git a/modules/@angular/facade/src/errors.ts b/modules/@angular/facade/src/errors.ts
index 71aa795b43..0fafc80431 100644
--- a/modules/@angular/facade/src/errors.ts
+++ b/modules/@angular/facade/src/errors.ts
@@ -6,6 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+/**
+ * Convenience to throw an Error with 'unimplemented' as the message.
+ */
 export function unimplemented(): any {
   throw new Error('unimplemented');
 }