diff --git a/assets/wire/components/fields/DurationLabel.tsx b/assets/wire/components/fields/DurationLabel.tsx
index 4ad915d26..78f0a561f 100644
--- a/assets/wire/components/fields/DurationLabel.tsx
+++ b/assets/wire/components/fields/DurationLabel.tsx
@@ -17,11 +17,11 @@ export function DurationLabel (props: IProps) {
         return null;
     }
 
-    function zeroPad(number: number) {
+    function zeroPad(number: number):string {
         if (number.toString().length < 2) {
             return `0${number}`;
         } else {
-            return number;
+            return number.toString();
         }
     }