@@ -87,10 +87,13 @@ func (opts *ListOpts) Len() int {

 type ValidatorFctType func(val string) (string, error)

 func ValidateAttach(val string) (string, error) {

-	if val != "stdin" && val != "stdout" && val != "stderr" {

-		return val, fmt.Errorf("Unsupported stream name: %s", val)

+	s := strings.ToLower(val)

+	for _, str := range []string{"stdin", "stdout", "stderr"} {

+		if s == str {

+			return s, nil

+		}

 	}

-	return val, nil

+	return val, fmt.Errorf("valid streams are STDIN, STDOUT and STDERR.")

 }

 func ValidateLink(val string) (string, error) {