diff --git a/search_api.module b/search_api.module
index 6253221..775e3d7 100644
--- a/search_api.module
+++ b/search_api.module
@@ -647,8 +647,9 @@ function search_api_search_api_index_insert(SearchApiIndex $index) {
  * Implements hook_search_api_index_update().
  */
 function search_api_search_api_index_update(SearchApiIndex $index) {
-  // Call the datasource update function with the table this module provides.
+  // Call the datasource update function with the tables this module provides.
   search_api_index_update_datasource($index, 'search_api_item');
+  search_api_index_update_datasource($index, 'search_api_item_string_id');
 
   // If the server was changed, we have to call the appropriate service class
   // hook methods.