diff --git a/aclocal/ax_lib_zlib.m4 b/aclocal/ax_lib_zlib.m4
index be4b6bb..8c10ab4 100644
--- a/aclocal/ax_lib_zlib.m4
+++ b/aclocal/ax_lib_zlib.m4
@@ -25,6 +25,11 @@
 dnl @category C
 dnl @version 2007-09-12
 dnl @license AllPermissive
+dnl
+dnl Copyright (C) 2009 David Reiss
+dnl Copying and distribution of this file, with or without modification,
+dnl are permitted in any medium without royalty provided the copyright
+dnl notice and this notice are preserved.
 
 dnl Input: ax_zlib_path, WANT_ZLIB_VERSION
 dnl Output: success=yes/no