diff --git a/moment/moment-external-tests.ts b/moment/moment-external-tests.ts
index ced06cdbf..1b1d083ba 100644
--- a/moment/moment-external-tests.ts
+++ b/moment/moment-external-tests.ts
@@ -195,6 +195,10 @@ moment.isMoment();
 moment.isMoment(new Date());
 moment.isMoment(moment());
 
+moment.isDuration();
+moment.isDuration(new Date());
+moment.isDuration(moment.duration());
+
 moment.localeData('fr');
 moment(1316116057189).fromNow();
 
diff --git a/moment/moment-tests.ts b/moment/moment-tests.ts
index d58a27fe3..dc11eeac8 100644
--- a/moment/moment-tests.ts
+++ b/moment/moment-tests.ts
@@ -195,6 +195,10 @@ moment.isMoment();
 moment.isMoment(new Date());
 moment.isMoment(moment());
 
+moment.isDuration();
+moment.isDuration(new Date());
+moment.isDuration(moment.duration());
+
 moment.localeData('fr');
 moment(1316116057189).fromNow();
 
diff --git a/moment/moment.d.ts b/moment/moment.d.ts
index 4d315946b..6bd041c5c 100644
--- a/moment/moment.d.ts
+++ b/moment/moment.d.ts
@@ -399,6 +399,8 @@ declare module moment {
         invalid(parsingFlags?: Object): Moment;
         isMoment(): boolean;
         isMoment(m: any): boolean;
+        isDuration(): boolean;
+        isDuration(d: any): boolean;
 
         // Deprecated in 2.8.0.
         lang(language?: string): string;