--- a/configure.ac
+++ b/configure.ac
@@ -952,8 +952,9 @@ dnl Check for %qu format (FreeBSD 4.x)
 dnl FreeBSD 4.x does not support %llu
 AC_MSG_CHECKING(for long long format)
 AC_RUN_IFELSE([AC_LANG_SOURCE([[
+#include <stdio.h>
 #include <sys/types.h>
-int main()
+int main(void)
 {
         uint64_t i;