diff --git a/src/Element/CardExpiration.php b/src/Element/CardExpiration.php
index 02a5554..9c673d7 100644
--- a/src/Element/CardExpiration.php
+++ b/src/Element/CardExpiration.php
@@ -90,7 +90,7 @@ class CardExpiration extends FormElement {
    * @return bool
    */
   public static function dateIsValid($value) {
-    if (!Unicode::strlen($value)) {
+    if (mb_strlen($value)) {
       return FALSE;
     }
 
diff --git a/src/Element/CardNumber.php b/src/Element/CardNumber.php
index c364d18..c5fb97f 100644
--- a/src/Element/CardNumber.php
+++ b/src/Element/CardNumber.php
@@ -103,7 +103,7 @@ class CardNumber extends FormElement {
     }
 
     // Set the string length and parity
-    $cardnumber_length = Unicode::strlen($value);
+    $cardnumber_length = mb_strlen($value);
 
     if ($cardnumber_length < 14 || $cardnumber_length > 16) {
       return FALSE;