diff --git a/library/Zend/Filter/StringTrim.php b/library/Zend/Filter/StringTrim.php
index 4f86d89e2c..e0e7b19f97 100644
--- a/library/Zend/Filter/StringTrim.php
+++ b/library/Zend/Filter/StringTrim.php
@@ -95,6 +95,10 @@ public function setCharList($charList)
      */
     public function filter($value)
     {
+        if (!is_string($value)) {
+            return $value;
+        }
+        
         if (null === $this->_charList) {
             return $this->_unicodeTrim((string) $value);
         } else {