diff --git a/chrome/content/zotero/xpcom/sync/syncRunner.js b/chrome/content/zotero/xpcom/sync/syncRunner.js
index edc23cb2c..bfdf16c8b 100644
--- a/chrome/content/zotero/xpcom/sync/syncRunner.js
+++ b/chrome/content/zotero/xpcom/sync/syncRunner.js
@@ -97,11 +97,16 @@ Zotero.Sync.Runner_Module = function (options = {}) {
 	 * @param {Function}  [options.onError]           Function to pass errors to instead of
 	 *                                                handling internally (used for testing)
 	 */
-	this.sync = Zotero.serial(Zotero.Promise.coroutine(function* (options = {}) {
+	this.sync = Zotero.serial(function (options = {}) {
+		return this._sync(options);
+	});
+	
+	
+	this._sync = Zotero.Promise.coroutine(function* (options) {
 		// Clear message list
 		_errors = [];
 		
-		// Shouldn't be possible
+		// Shouldn't be possible because of serial()
 		if (_syncInProgress) {
 			let msg = Zotero.getString('sync.error.syncInProgress');
 			let e = new Zotero.Error(msg, 0, { dialogButtonText: null, frontWindowOnly: true });
@@ -233,14 +238,14 @@ Zotero.Sync.Runner_Module = function (options = {}) {
 			if (options.restartSync) {
 				delete options.restartSync;
 				Zotero.debug("Restarting sync");
-				yield this.sync(options);
+				yield this._sync(options);
 				return;
 			}
 			
 			Zotero.debug("Done syncing");
 			Zotero.Notifier.trigger('finish', 'sync', librariesToSync || []);
 		}
-	}));
+	});
 	
 	
 	/**