diff --git a/acinclude.m4 b/acinclude.m4
index 3619d49..6658523 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -16,7 +16,7 @@ dnl Based on David Arnold's autoconf suggestion in the threads faq.
 dnl
 dnl @author Caolan McNamara <caolan@skynet.ie>
 dnl
-AC_DEFUN(AC_caolan_FUNC_WHICH_GETHOSTBYNAME_R,
+AC_DEFUN([AC_caolan_FUNC_WHICH_GETHOSTBYNAME_R],
 [AC_CACHE_CHECK(for which type of gethostbyname_r, ac_cv_func_which_gethostname_r, [
 AC_CHECK_FUNC(gethostbyname_r, [
         AC_TRY_COMPILE([