diff --git a/acinclude.m4 b/acinclude.m4
index 44c386a..4ff672e 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -11,7 +11,7 @@
 [#]line __oline__ "configure"
 #include "confdefs.h"
 [$1]
-int main() {
+int main(void) {
 [$2]
 ; return 0; }
 EOF