diff --git a/taglib/mpeg/id3v2/frames/commentsframe.cpp b/taglib/mpeg/id3v2/frames/commentsframe.cpp
index 55bded7f..fc91d5e6 100644
--- a/taglib/mpeg/id3v2/frames/commentsframe.cpp
+++ b/taglib/mpeg/id3v2/frames/commentsframe.cpp
@@ -154,7 +154,7 @@ ByteVector CommentsFrame::renderFields() const
   ByteVector v;
 
   v.append(char(d->textEncoding));
-  v.append(d->language.size() == 3 ? d->language : "   ");
+  v.append(d->language.size() == 3 ? d->language : "XXX");
   v.append(d->description.data(d->textEncoding));
   v.append(textDelimiter(d->textEncoding));
   v.append(d->text.data(d->textEncoding));