diff --git a/README.md b/README.md
index 718f1c2..562bdd9 100644
--- a/README.md
+++ b/README.md
@@ -22,10 +22,10 @@ Features:
   pick up most of the podcast text straight from the tags in the file (such as
   the artist, title and comment tags.)
 
-* supports MP3, MP4, and M4A files
+* supports MP3, MP4, M4A and M4B files
 
 * dir2cast will automatically use the ID3 fields from your files for the Author,
-  Title, etc. ID3v2 is supported, as are the regular tags found in MP4 and M4A
+  Title, etc. ID3v2 is supported, as are the usual tags found in MP4 / M4A / M4B
   files. (Uses getID3, which is bundled with dir2cast.)
 
 * dir2cast will automatically use the cover art embedded in your file as well.
@@ -81,7 +81,7 @@ Please note: the config file will make more sense if you read all of this `READM
 before trying the installation instructions.
 
 dir2cast is quite flexible but the general idea is that you add cover art and
-tags to your media files - mp3, mp4 or m4a currently supported - and then the
+tags to your media files (mp3, mp4, m4a and m4b currently supported) and then the
 podcast that it generates uses the tags from your files.
 
 1. Edit `dir2cast.ini` to your taste.
diff --git a/dir2cast.php b/dir2cast.php
index 4dfb29c..45cc1ef 100644
--- a/dir2cast.php
+++ b/dir2cast.php
@@ -1200,6 +1200,7 @@ public function addItem($filename)
                 break;
 
             case 'm4a':
+            case 'm4b':
                 $this->addRssFileItem(new M4A_RSS_Item($filename));
                 break;