diff --git a/chrome/content/zotero/xpcom/storage/storageEngine.js b/chrome/content/zotero/xpcom/storage/storageEngine.js
index 255d8d6d15..8f82cdc3b0 100644
--- a/chrome/content/zotero/xpcom/storage/storageEngine.js
+++ b/chrome/content/zotero/xpcom/storage/storageEngine.js
@@ -327,7 +327,8 @@ Zotero.Sync.Storage.Engine.prototype.queueItem = Zotero.Promise.coroutine(functi
 			return;
 		
 		default:
-			throw new Error("Invalid sync state " + item.attachmentSyncState);
+			throw new Error("Invalid sync state " + item.attachmentSyncState + " for item "
+				+ item.libraryKey);
 	}
 	
 	if (type == 'upload') {