diff --git a/os/gcmd/gcmd_command_object.go b/os/gcmd/gcmd_command_object.go
index fa3a98f5a..efd14cb4b 100644
--- a/os/gcmd/gcmd_command_object.go
+++ b/os/gcmd/gcmd_command_object.go
@@ -57,6 +57,9 @@ func NewFromObject(object interface{}) (rootCmd *Command, err error) {
 		rootCommandName = gmeta.Get(object, tagNameRoot).String()
 		subCommands     []*Command
 	)
+	if rootCommandName == "" {
+		rootCommandName = rootCmd.Name
+	}
 	for i := 0; i < originValueAndKind.InputValue.NumMethod(); i++ {
 		var (
 			method        = originValueAndKind.InputValue.Method(i)
diff --git a/util/gtag/gtag.go b/util/gtag/gtag.go
index 4dce4aab9..020f331b1 100644
--- a/util/gtag/gtag.go
+++ b/util/gtag/gtag.go
@@ -10,6 +10,7 @@
 package gtag
 
 import (
+	"fmt"
 	"regexp"
 	"sync"
 )
@@ -24,6 +25,9 @@ var (
 func Set(name, value string) {
 	mu.Lock()
 	defer mu.Unlock()
+	if _, ok := data[name]; ok {
+		panic(fmt.Sprintf(`value for tag "%s" already exists`, name))
+	}
 	data[name] = value
 }
 
@@ -32,6 +36,9 @@ func Sets(m map[string]string) {
 	mu.Lock()
 	defer mu.Unlock()
 	for k, v := range m {
+		if _, ok := data[k]; ok {
+			panic(fmt.Sprintf(`value for tag "%s" already exists`, k))
+		}
 		data[k] = v
 	}
 }