diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index cf2c552aeb5..81b217c506a 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2014-06-12  Kevin Ryde  <user42_kevin@yahoo.com.au>
+
+	* files.el (auto-mode-alist): Map .ad files to xdefaults-mode
+	(bug#17745).
+
 2014-06-12  Stefan Monnier  <monnier@iro.umontreal.ca>
 
 	* international/mule-cmds.el: Use lexical-binding.
diff --git a/lisp/files.el b/lisp/files.el
index 0b3e1d6f552..9017cc96703 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2440,7 +2440,7 @@ ARC\\|ZIP\\|LZH\\|LHA\\|ZOO\\|[JEW]AR\\|XPI\\|RAR\\|7Z\\)\\'" . archive-mode)
      ("/\\.\\(?:enigma\\|gltron\\|gtk\\|hxplayer\\|net\\|neverball\\|qt/.+\\|realplayer\\|scummvm\\|sversion\\|sylpheed/.+\\|xmp\\)rc\\'" . conf-mode)
      ("/\\.\\(?:gdbtkinit\\|grip\\|orbital/.+txt\\|rhosts\\|tuxracer/options\\)\\'" . conf-mode)
      ("/\\.?X\\(?:default\\|resource\\|re\\)s\\>" . conf-xdefaults-mode)
-     ("/X11.+app-defaults/" . conf-xdefaults-mode)
+     ("/X11.+app-defaults/\\|\\.ad\\'" . conf-xdefaults-mode)
      ("/X11.+locale/.+/Compose\\'" . conf-colon-mode)
      ;; this contains everything twice, with space and with colon :-(
      ("/X11.+locale/compose\\.dir\\'" . conf-javaprop-mode)