diff --git a/application/models/QuestionTheme.php b/application/models/QuestionTheme.php
index 17d877f3eb5..291b26cae58 100644
--- a/application/models/QuestionTheme.php
+++ b/application/models/QuestionTheme.php
@@ -54,7 +54,7 @@ public function rules()
                 'unique',
                 'caseSensitive' => false,
                 'criteria'      => [
-                    'condition' => '`extends`=:extends',
+                    'condition' => 'extends=:extends',
                     'params'    => [
                         ':extends' => $this->extends
                     ]