cmd/sgblog-comment-add/mail.go | 8 ++++----

diff --git a/cmd/sgblog-comment-add/mail.go b/cmd/sgblog-comment-add/mail.go
index 9624884e93027dfb839c8cf77d137b8b98ddbc56c01a97ec1a8b576131b438a5..206f175000623aa22e38c5971f460bc865c126fb8a3a5ac20cfd28e68fd38e29 100644
--- a/cmd/sgblog-comment-add/mail.go
+++ b/cmd/sgblog-comment-add/mail.go
@@ -39,10 +39,10 @@ 	_, params, err := mime.ParseMediaType(ct)
 	if err != nil {
 		return nil, err
 	}
-	if c := strings.ToLower(params["charset"]); !(c == "" ||
-		c == "utf-8" ||
-		c == "iso-8859-1" ||
-		c == "us-ascii") {
+	if c := strings.ToLower(params["charset"]); c != "" &&
+		c != "utf-8" &&
+		c != "iso-8859-1" &&
+		c != "us-ascii" {
 		return nil, errors.New("only utf-8/iso-8859-1/us-ascii charsets supported")
 	}
 	switch cte {