diff --git a/lib/register.lib.php b/lib/register.lib.php
index 303612bea..93ed1071c 100644
--- a/lib/register.lib.php
+++ b/lib/register.lib.php
@@ -112,12 +112,16 @@ function valid_mb_email($reg_mb_email)
 function prohibit_mb_email($reg_mb_email)
 {
     global $config;
+
     list($id, $domain) = explode("@", $reg_mb_email);
     $email_domains = explode("\n", trim($config['cf_prohibit_email']));
-    for ($i=0; $i<count($email_domains); $i++) {
-        if (strtolower(settype($domain, "string")) == strtolower(settype($email_domains[$i], "string")))
-            return "$domain 메일은 사용할 수 없습니다.";
-    }
+    $email_domains = array_map('trim', $email_domains);
+    $email_domains = array_map('strtolower', $email_domains);
+    $email_domain = strtolower($domain);
+
+    if (in_array($email_domain, $email_domains))
+        return "$domain 메일은 사용할 수 없습니다.";
+
     return "";
 }