diff --git a/src/Oro/ORM/Query/AST/Functions/String/DateFormat.php b/src/Oro/ORM/Query/AST/Functions/String/DateFormat.php
index f69f4375150..596bf2492c6 100644
--- a/src/Oro/ORM/Query/AST/Functions/String/DateFormat.php
+++ b/src/Oro/ORM/Query/AST/Functions/String/DateFormat.php
@@ -93,7 +93,7 @@ public function parse(Parser $parser)
 
     private function validateFormat(Parser $parser): void
     {
-        $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 $unsupportedFormat) {
             if (false !== \strpos($format, $unsupportedFormat)) {