diff --git a/README.md b/README.md
index 1fb02fc..834e106 100644
--- a/README.md
+++ b/README.md
@@ -24,13 +24,24 @@ if err != nil {
 	os.Exit(1)
 }
 p.AddIPAddr(ra)
-p.AddHandler("receive", func(addr *net.IPAddr, rtt time.Duration) {
+err = p.AddHandler("receive", func(addr *net.IPAddr, rtt time.Duration) {
 	fmt.Printf("IP Addr: %s receive, RTT: %v\n", addr.String(), rtt)
 })
-p.AddHandler("idle", func() {
+if err != nil {
+	fmt.Println(err)
+	os.Exit(1)
+}
+err = p.AddHandler("idle", func() {
 	fmt.Println("finish")
 })
-p.Run()
+if err != nil {
+	fmt.Println(err)
+	os.Exit(1)
+}
+err = p.Run()
+if err != nil {
+	fmt.Println(err)
+}
 ```
 
 It sends an ICMP packet and wait a response. If it receives a response, it
diff --git a/fastping.go b/fastping.go
index 69838df..fcf5ec7 100644
--- a/fastping.go
+++ b/fastping.go
@@ -15,13 +15,24 @@
 //		os.Exit(1)
 //	}
 //	p.AddIPAddr(ra)
-//	p.AddHandler("receive", func(addr *net.IPAddr, rtt time.Duration) {
+//	err = p.AddHandler("receive", func(addr *net.IPAddr, rtt time.Duration) {
 //		fmt.Printf("IP Addr: %s receive, RTT: %v\n", addr.String(), rtt)
 //	})
-//	p.AddHandler("idle", func() {
+//	if err != nil {
+//		fmt.Println(err)
+//		os.Exit(1)
+//	}
+//	err = p.AddHandler("idle", func() {
 //		fmt.Println("finish")
 //	})
-//	p.Run()
+//	if err != nil {
+//		fmt.Println(err)
+//		os.Exit(1)
+//	}
+//	err = p.Run()
+//	if err != nil {
+//		fmt.Println(err)
+//	}
 //
 // It sends an ICMP packet and wait a response. If it receives a response,
 // it calls "receive" callback. After that, MaxRTT time passed, it calls