diff --git a/lib/imap.js b/lib/imap.js
index 7d43915..2ff26e9 100644
--- a/lib/imap.js
+++ b/lib/imap.js
@@ -845,7 +845,8 @@ ImapConnection.prototype.append = function(data, options, cb) {
   if (options.flags) {
     if (!Array.isArray(options.flags))
       options.flags = [options.flags];
-    cmd += " (\\" + options.flags.join(' \\') + ")";
+    if (options.flags.length > 0)
+      cmd += " (\\" + options.flags.join(' \\') + ")";
   }
   if (options.date) {
     if (!isDate(options.date))