diff --git a/acx_nlnetlabs.m4 b/acx_nlnetlabs.m4
index 719112645..90f1315bb 100644
--- a/acx_nlnetlabs.m4
+++ b/acx_nlnetlabs.m4
@@ -2,7 +2,8 @@
 # Copyright 2009, Wouter Wijngaards, NLnet Labs.   
 # BSD licensed.
 #
-# Version 24
+# Version 25
+# 2013-07-18 Enable ACX_CHECK_COMPILER_FLAG to test for -Wstrict-prototypes
 # 2013-06-25 FLTO has --disable-flto option.
 # 2013-05-03 Update W32_SLEEP for newer mingw that links but not defines it.
 # 2013-03-22 Fix ACX_RSRC_VERSION for long version numbers.
@@ -119,7 +120,7 @@ AC_MSG_CHECKING(whether $CC supports -$1)
 cache=`echo $1 | sed 'y%.=/+-%___p_%'`
 AC_CACHE_VAL(cv_prog_cc_flag_$cache,
 [
-echo 'void f(){}' >conftest.c
+echo 'void f(void){}' >conftest.c
 if test -z "`$CC $CPPFLAGS $CFLAGS -$1 -c conftest.c 2>&1`"; then
 eval "cv_prog_cc_flag_$cache=yes"
 else