diff --git a/types/moment-duration-format/index.d.ts b/types/moment-duration-format/index.d.ts
index a3ce7bb300..34179e6dc4 100644
--- a/types/moment-duration-format/index.d.ts
+++ b/types/moment-duration-format/index.d.ts
@@ -7,7 +7,7 @@ import * as moment from "moment";
 
 declare module "moment" {
     interface Duration {
-        format(template: string, precision?: string, settings?: DurationFormatSettings): string;
+        format(template: string, precision?: number, settings?: DurationFormatSettings): string;
     }
 
     interface DurationFormatSettings {