diff --git a/chrome/content/zotero/xpcom/sync/syncEngine.js b/chrome/content/zotero/xpcom/sync/syncEngine.js
index 2f5b60378..7086a27fa 100644
--- a/chrome/content/zotero/xpcom/sync/syncEngine.js
+++ b/chrome/content/zotero/xpcom/sync/syncEngine.js
@@ -824,7 +824,13 @@ Zotero.Sync.Data.Engine.prototype._startUpload = Zotero.Promise.coroutine(functi
 		let unsyncedKeys = ids.map(id => objectsClass.getLibraryAndKeyFromID(id).key);
 		let origUnsynced = unsyncedKeys; // TEMP
 		let queueKeys = yield Zotero.Sync.Data.Local.getObjectsFromSyncQueue(objectType, this.libraryID);
+		let num = unsyncedKeys.length;
 		unsyncedKeys = Zotero.Utilities.arrayDiff(unsyncedKeys, queueKeys);
+		if (unsyncedKeys.length < num) {
+			Zotero.debug(`Skipping ${num - unsyncedKeys.length} key(s) in sync queue`);
+			Zotero.debug(Zotero.Utilities.arrayDiff(unsyncedKeys, queueKeys));
+		}
+		
 		// TEMP
 		//ids = unsyncedKeys.map(key => objectsClass.getIDFromLibraryAndKey(this.libraryID, key));
 		let missing = [];