diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index a53e7e7..cd74d6d 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -1038,7 +1038,11 @@
 			$domain = defined('INTL_IDNA_VARIANT_UTS46')
 				? idn_to_ascii($domain, 0, INTL_IDNA_VARIANT_UTS46)
 				: idn_to_ascii($domain);
-			$email = $account.'@'.$domain;
+
+			if ($domain !== FALSE)
+			{
+				$email = $account.'@'.$domain;
+			}
 		}
 
 		return (bool) filter_var($email, FILTER_VALIDATE_EMAIL);
@@ -1859,7 +1863,11 @@
 			$domain = defined('INTL_IDNA_VARIANT_UTS46')
 				? idn_to_ascii($domain, 0, INTL_IDNA_VARIANT_UTS46)
 				: idn_to_ascii($domain);
-			$email = $account.'@'.$domain;
+
+			if ($domain !== FALSE)
+			{
+				$email = $account.'@'.$domain;
+			}
 		}
 
 		return (filter_var($email, FILTER_VALIDATE_EMAIL) === $email && preg_match('#\A[a-z0-9._+-]+@[a-z0-9.-]{1,253}\z#i', $email));
diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index 6a97ee5..27187df 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -1234,7 +1234,11 @@
 			$domain = defined('INTL_IDNA_VARIANT_UTS46')
 				? idn_to_ascii($matches[2], 0, INTL_IDNA_VARIANT_UTS46)
 				: idn_to_ascii($matches[2]);
-			$str = $matches[1].'@'.$domain;
+
+			if ($domain !== FALSE)
+			{
+				$str = $matches[1].'@'.$domain;
+			}
 		}
 
 		return (bool) filter_var($str, FILTER_VALIDATE_EMAIL);