diff --git a/src/Common/AssertionConcern.php b/src/Common/AssertionConcern.php
index eaceb2e..cbe704d 100644
--- a/src/Common/AssertionConcern.php
+++ b/src/Common/AssertionConcern.php
@@ -85,7 +85,7 @@ protected function assertStateTrue($aBoolean, $aMessage)
 
     protected function assertArgumentLength($aString, $aMaximum, $aMessage)
     {
-        $length = count(trim($aString));
+        $length = strlen(trim($aString));
 
         if ($length > $aMaximum) {
             throw new InvalidArgumentException($aMessage);