diff --git a/src/index.ts b/src/index.ts
index 3b413f8..db33654 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -13,13 +13,17 @@ export class ExecuteTooManyTimesError extends Error {
   }
 }
 
-export function pending(n: number, fn: Callback) {
+export function pending(fn: Callback, n: number): (err?: Error) => void;
+export function pending(n: number, fn: Callback): (err?: Error) => void;
+export function pending(n: number | Callback, fn: Callback | number): (err?: Error) => void {
+  let _fn: Callback;
   if (typeof n === 'function') {
     // keep compatibility for old version
     // pending(fn, n)
-    const tmp = n;
-    n = fn as unknown as number;
-    fn = tmp as Callback;
+    _fn = n;
+    n = fn as number;
+  } else {
+    _fn = fn as Callback;
   }
 
   let called = false;
@@ -32,11 +36,11 @@ export function pending(n: number, fn: Callback) {
     }
     if (err) {
       called = true;
-      return fn(err);
+      return _fn(err);
     }
     times++;
     if (times === n) {
-      fn();
+      _fn();
     } else if (times > n) {
       const err = new ExecuteTooManyTimesError(n, times);
       err.stack += '\n' + callStack.stack;
diff --git a/test/pedding.test.ts b/test/pedding.test.ts
index 8dd4770..83695eb 100644
--- a/test/pedding.test.ts
+++ b/test/pedding.test.ts
@@ -19,7 +19,7 @@ describe('test/pedding.test.ts', () => {
   });
 
   it('should called pedding(done, 100) then done()', done => {
-    done = pedding(done as any, 100 as any);
+    done = pedding(done, 100);
     for (let i = 0; i < 100; i++) {
       done();
     }