diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 4815ac2a482..f9f3aad9ab2 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,7 @@
+2013-01-04  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+	* files.texi (File Attributes): Undocument return format of file-acl.
+
 2013-01-03  Glenn Morris  <rgm@gnu.org>
 
 	* processes.texi (System Processes):
diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index c323a6e72ad..114eb1f38ea 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -1363,7 +1363,7 @@ security APIs.
 
 @defun file-acl filename
 This function returns the ACL entries of the file @var{filename}.  The
-return value is a platform-dependent string containing the textual
+return value is a platform-dependent object containing some
 representation of the ACL entries.  Don't use it for anything except
 passing it to the @code{set-file-acl} function (@pxref{Changing Files,
 set-file-acl}).
diff --git a/src/ChangeLog b/src/ChangeLog
index 7342f7c6add..fa27e299ad7 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2013-01-04  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+	* fileio.c (Ffile_acl): Undocument return format.
+
 2013-01-02  Glenn Morris  <rgm@gnu.org>
 
 	* keymap.c (Fkey_description): Doc fix.  (Bug#13323)
diff --git a/src/fileio.c b/src/fileio.c
index 05f615f0c88..5e9b36ee44a 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3084,11 +3084,11 @@ or if Emacs was not compiled with SELinux support.  */)
 }
 
 DEFUN ("file-acl", Ffile_acl, Sfile_acl, 1, 1, 0,
-       doc: /* Return ACL entries of file named FILENAME, as a string.
+       doc: /* Return ACL entries of file named FILENAME.
+The entries are returned in a format suitable for use in `set-file-acl'
+but is otherwise undocumented and subject to change.
 Return nil if file does not exist or is not accessible, or if Emacs
-was unable to determine the ACL entries.  The latter can happen for
-local files if Emacs was not compiled with ACL support, or for remote
-files if the file handler returns nil for the file's ACL entries.  */)
+was unable to determine the ACL entries.  */)
   (Lisp_Object filename)
 {
   Lisp_Object absname;