diff --git a/types/index.d.ts b/types/index.d.ts
index b2864e017..55b3f3304 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -65,7 +65,7 @@ declare namespace dayjs {
 
     format(template?: string): string
 
-    diff(date: ConfigType, unit: QUnitType | OpUnitType, float?: boolean): number
+    diff(date: ConfigType, unit?: QUnitType | OpUnitType, float?: boolean): number
 
     valueOf(): number