diff --git a/m4/ac_attribute.m4 b/m4/ac_attribute.m4
index f063e1ff..60a22f93 100644
--- a/m4/ac_attribute.m4
+++ b/m4/ac_attribute.m4
@@ -1,3 +1,16 @@
+dnl Copyright (C) 2004-2008 Kim Woelders
+dnl This code is public domain and can be freely used or copied.
+dnl Originally snatched from somewhere...
+
+dnl Macro for checking if the compiler supports __atribute__
+
+dnl Usage: AC_C___ATTRIBUTE__
+
+dnl Call AC_DEFINE for HAVE___ATTRIBUTE__ and __UNUSED__.
+dnl If the compiler supports __attribute__, HAVE___ATTRIBUTE__ is
+dnl defined to 1 and __UNUSED__ is defined to __attribute__((unused))
+dnl otherwise, HAVE___ATTRIBUTE__ is not defined and __UNUSED__ is
+dnl defined to nothing.
 
 AC_DEFUN([AC_C___ATTRIBUTE__],
 [