diff --git a/chrome/content/zotero/xpcom/storage/storageEngine.js b/chrome/content/zotero/xpcom/storage/storageEngine.js
index 1900b9dba9..dbd40786c5 100644
--- a/chrome/content/zotero/xpcom/storage/storageEngine.js
+++ b/chrome/content/zotero/xpcom/storage/storageEngine.js
@@ -23,6 +23,7 @@
     ***** END LICENSE BLOCK *****
 */
 
+var { ConcurrentCaller } = ChromeUtils.importESModule("resource://zotero/concurrentCaller.mjs");
 
 if (!Zotero.Sync.Storage) {
 	Zotero.Sync.Storage = {};