diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 1541bb950f0..56b2326b1fe 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2001-06-23  Eli Zaretskii  <eliz@is.elta.co.il>
+
+	* files.el (auto-mode-alist): Add configure.ac (autoconf).  From
+	Karl Eichwalder <ke@suse.de>.
+
 2001-06-23  Richard M. Stallman  <rms@gnu.org>
 
 	* emacs-lisp/lisp-mode.el (eval-last-sexp): Doc fix.
diff --git a/lisp/files.el b/lisp/files.el
index d0cbc2cc417..977da75e4a9 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -1455,7 +1455,7 @@ in that case, this function acts as if `enable-local-variables' were t."
      ("\\.\\(diffs?\\|patch\\|rej\\)\\'" . diff-mode)
      ("\\.\\(dif\\|pat\\)\\'" . diff-mode) ; for MSDOG
      ("\\.[eE]?[pP][sS]\\'" . ps-mode)
-     ("configure\\.in\\'" . autoconf-mode)
+     ("configure\\.\\(ac\\|in\\)\\'" . autoconf-mode)
      ("BROWSE\\'" . ebrowse-tree-mode)
      ("\\.ebrowse\\'" . ebrowse-tree-mode)
      ("#\\*mail\\*" . mail-mode)