diff --git a/includes/rules.state.inc b/includes/rules.state.inc
index a4150e7..b7896c7 100644
--- a/includes/rules.state.inc
+++ b/includes/rules.state.inc
@@ -617,7 +617,9 @@ class RulesData  {
    */
   public static function addSiteMetadata(EntityMetadataWrapper $wrapper, $property_info) {
     $site_info = entity_get_property_info('site');
-    $property_info['properties'] += $site_info['properties'];
+    if (!empty($site_info['properties'])) {
+      $property_info['properties'] += $site_info['properties'];
+    }
     // Also invoke the usual callback for altering metadata, in case actions
     // have specified further metadata.
     return RulesData::applyMetadataAssertions($wrapper, $property_info);