--- a/lisp/packages.el	Tue Feb 09 00:30:59 2010 -0600
+++ b/lisp/packages.el	Tue Feb 09 03:53:52 2010 -0600
@@ -385,8 +385,10 @@
 (defun packages-find-installation-package-directories (roots)
   "Find the package directories in the XEmacs installation.
 ROOTS is a list of installation roots."
-  (union (paths-find-version-directories roots (list "") nil nil nil t)
-         (paths-find-site-directories roots (list "") nil) :test #'equal))
+  (delete-duplicates
+   (nconc (paths-find-version-directories roots (list "") nil nil nil t)
+          (paths-find-site-directories roots (list "") nil))
+   :test #'equal))
 
 (defun packages-find-package-hierarchies (package-directories &optional envvar default)
   "Find package hierarchies in a list of package directories.