diff --git a/lib/detect-port.js b/lib/detect-port.js
index 3859484..9d3cbf9 100644
--- a/lib/detect-port.js
+++ b/lib/detect-port.js
@@ -23,10 +23,10 @@ module.exports = function() {
       reject('wrong number of arguments');
     }
 
-    const port = args[0];
+    const port = parseInt(args[0], 10);
 
-    if (typeof port !== 'number') {
-      reject(`wrong type of arguments with: ${port}`);
+    if (isNaN(port)) {
+      reject(`wrong type of arguments with: '${args[0]}'`);
     }
 
     const loop = port => {
diff --git a/package.json b/package.json
index d0b03fb..889c7a6 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "detect-port",
-  "version": "1.0.4",
+  "version": "1.0.5",
   "description": "detect available port",
   "keywords": [
     "detect",
diff --git a/test/detect-port.test.js b/test/detect-port.test.js
index 391e611..1f263e5 100644
--- a/test/detect-port.test.js
+++ b/test/detect-port.test.js
@@ -28,11 +28,20 @@ describe('detect port test', () => {
     });
   });
 
-  it('callback with wrong arguments', done => {
-    detectPort('8080', err => {
+  it('callback with string arg', done => {
+    const _port = '8080';
+    detectPort(_port, (err, port) => {
       if (err) {
-        err.should.containEql('wrong type of arguments');
+        console.log(err);
       }
+      port.should.within(parseInt(_port, 10), 65535);
+      done();
+    });
+  });
+
+  it('callback with wrong arguments', done => {
+    detectPort('oooo', err => {
+      err.should.containEql('wrong type of arguments');
       done();
     });
   });
@@ -73,7 +82,7 @@ describe('detect port test', () => {
 
   it('generator with wrong arguments', function *() {
     try {
-      yield detectPort('8080');
+      yield detectPort('oooo');
     } catch (err) {
       err.should.containEql('wrong type of arguments');
     }