diff --git a/src/Oro/ORM/Query/AST/Functions/String/DateFormat.php b/src/Oro/ORM/Query/AST/Functions/String/DateFormat.php
index 5f64a3ebdd6..f5464c45bac 100644
--- a/src/Oro/ORM/Query/AST/Functions/String/DateFormat.php
+++ b/src/Oro/ORM/Query/AST/Functions/String/DateFormat.php
@@ -102,7 +102,7 @@ public function parse(Parser $parser)
      */
     private function validateFormat(Parser $parser)
     {
-        $format = str_replace('%%', '', $this->parameters[self::FORMAT_KEY]);
+        $format = str_replace('%%', '', (string)$this->parameters[self::FORMAT_KEY]);
         $unsupportedFormats = array_diff(self::$knownFormats, self::$supportedFormats);
         foreach ($unsupportedFormats as $unsupportedFormat) {
             if (strpos($format, $unsupportedFormat) !== false) {