diff --git a/README b/README
index 2c570e1d..5f029c82 100644
--- a/README
+++ b/README
@@ -1,8 +1,9 @@
 Notmuch - thread-based email index, search and tagging.
 
 Notmuch is a system for indexing, searching, reading, and tagging
-large collections of email messages. It uses the Xapian library to
-provide fast, full-text search with a convenient search syntax.
+large collections of email messages in maildir or mh format. It uses
+the Xapian library to provide fast, full-text search with a convenient
+search syntax.
 
 Notmuch is free software, released under the GNU General Public
 License version 3 (or later).