diff --git a/chrome/content/zotero/xpcom/storage/storageRequest.js b/chrome/content/zotero/xpcom/storage/storageRequest.js
index 573b4ebb91..f1b0a6ae80 100644
--- a/chrome/content/zotero/xpcom/storage/storageRequest.js
+++ b/chrome/content/zotero/xpcom/storage/storageRequest.js
@@ -37,7 +37,6 @@
  * @param {Function|Function[]} [options.onStop]
  */
 Zotero.Sync.Storage.Request = function (options) {
-	if (!options.engine) throw new Error("engine must be provided");
 	if (!options.type) throw new Error("type must be provided");
 	if (!options.libraryID) throw new Error("libraryID must be provided");
 	if (!options.name) throw new Error("name must be provided");
diff --git a/chrome/content/zotero/xpcom/storage/zfs.js b/chrome/content/zotero/xpcom/storage/zfs.js
index 0d3e0a9f73..511f020578 100644
--- a/chrome/content/zotero/xpcom/storage/zfs.js
+++ b/chrome/content/zotero/xpcom/storage/zfs.js
@@ -285,7 +285,7 @@ Zotero.Sync.Storage.Mode.ZFS.prototype = {
 			}
 			if (skip) {
 				// Stop trying to upload files if there's very little storage remaining
-				if (remaining < Zotero.Sync.Storage.Local.STORAGE_REMAINING_MINIMUM) {
+				if (request.engine && remaining < Zotero.Sync.Storage.Local.STORAGE_REMAINING_MINIMUM) {
 					Zotero.debug(`${remaining} MB remaining in storage -- skipping further uploads`);
 					request.engine.stop('upload');
 				}
@@ -306,7 +306,7 @@ Zotero.Sync.Storage.Mode.ZFS.prototype = {
 		catch (e) {
 			// Stop trying to upload files if we hit a quota error and there's very little space
 			// remaining. If there's more space, we keep going, because it might just be a big file.
-			if (e.error == Zotero.Error.ERROR_ZFS_OVER_QUOTA) {
+			if (request.engine && e.error == Zotero.Error.ERROR_ZFS_OVER_QUOTA) {
 				let remaining = Zotero.Sync.Storage.Local.storageRemainingForLibrary.get(item.libraryID);
 				if (remaining < Zotero.Sync.Storage.Local.STORAGE_REMAINING_MINIMUM) {
 					Zotero.debug(`${remaining} MB remaining in storage -- skipping further uploads`);