diff --git a/aclocal.m4 b/aclocal.m4
index f3a0ceb0e..d0428a9b9 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -106,8 +106,8 @@ dnl
 dnl check for fullly working void
 dnl
 AC_DEFUN(SUDO_FULL_VOID, [AC_MSG_CHECKING(for full void implementation)
-AC_TRY_COMPILE(, [void *foo;
-foo = 0;], AC_DEFINE(VOID, void)
+AC_TRY_COMPILE(, [void *foo = NULL;
+foo += 1;], AC_DEFINE(VOID, void)
 AC_MSG_RESULT(yes), AC_DEFINE(VOID, char)
 AC_MSG_RESULT(no))])
 dnl