diff --git a/src/Plugin/WebformElement/WebformCompositeBase.php b/src/Plugin/WebformElement/WebformCompositeBase.php
 --- a/src/Plugin/WebformElement/WebformCompositeBase.php
 +++ b/src/Plugin/WebformElement/WebformCompositeBase.php
@@ -24,7 +24,7 @@ index f96d5745b..f826c90f9 100644
          $properties[$composite_key . '__unique'] = FALSE;
          $properties[$composite_key . '__unique_user'] = FALSE;
          $properties[$composite_key . '__unique_entity'] = FALSE;
-         $properties[$composite_key . '__unique_error'] = FALSE;
+         $properties[$composite_key . '__unique_error'] = '';
          $properties[$composite_key . '__placeholder'] = '';
        }
        $properties[$composite_key . '__access'] = TRUE;