diff --git a/lib/imap.js b/lib/imap.js
index d600991..1f50b96 100644
--- a/lib/imap.js
+++ b/lib/imap.js
@@ -587,7 +587,7 @@ ImapConnection.prototype.connect = function(loginCb) {
                 for (i=0,len=keywords.length; i<len; ++i)
                   permFlags.splice(permFlags.indexOf(keywords[i]), 1);
                 state.box.permFlags = permFlags.map(function(f) {
-                                        return f.substr(1);
+                                        return f.substr(1).toLowerCase();
                                       });
               }
             } else if (state.status === STATES.BOXSELECTED) {
@@ -1465,7 +1465,7 @@ ImapConnection.prototype._store = function(which, uids, flags, isAdding, cb) {
     if (!isKeywords) {
       if (flags[i][0] === '\\')
         flags[i] = flags[i].substr(1);
-      if (this._state.box.permFlags.indexOf(flags[i]) === -1
+      if (this._state.box.permFlags.indexOf(flags[i].toLowerCase()) === -1
           || flags[i] === '*')
         throw new Error('The flag "' + flags[i]
                         + '" is not allowed by the server for this mailbox');