diff --git a/smtp.go b/smtp.go
index d8bca14..95e60e0 100644
--- a/smtp.go
+++ b/smtp.go
@@ -455,7 +455,7 @@ func (c *Client) Quit() error {
 	return c.Text.Close()
 }
 
-// validateLine checks to see if a line has CR or LF as per RFC 5321
+// validateLine checks to see if a line has CR or LF as per RFC 5321.
 func validateLine(line string) error {
 	if strings.ContainsAny(line, "\n\r") {
 		return errors.New("smtp: A line must not contain CR or LF")