diff --git a/library/Zend/Db/Statement.php b/library/Zend/Db/Statement.php
index 46d175c..763594d 100644
--- a/library/Zend/Db/Statement.php
+++ b/library/Zend/Db/Statement.php
@@ -208,7 +208,11 @@ protected function _stripQuoted($sql)
         // values and delimited identifiers stripped out
         // remove "foo\"bar"
         $sql = preg_replace("/\"(\\\\\"|[^\"])*\"/Us", '', $sql);
-
+        if ($sql === null) {
+            // this preg_replace call can return NULL in case of error (PREG_BACKTRACK_LIMIT_ERROR).
+            // In this case the result of this method will be an empty string.
+            return '';
+        }
         // get the character for delimited id quotes,
         // this is usually " but in MySQL is `
         $d = $this->_adapter->quoteIdentifier('a');
@@ -220,6 +224,11 @@ protected function _stripQuoted($sql)
         $de = preg_quote($de);
         // Note: $de and $d where never used..., now they are:
         $sql = preg_replace("/$d($de|\\\\{2}|[^$d])*$d/Us", '', $sql);
+        if ($sql === null) {
+            // this preg_replace call can return NULL in case of error (PREG_BACKTRACK_LIMIT_ERROR).
+            // In this case the result of this method will be an empty string.
+            return '';
+        }
         return $sql;
     }