[...]
  CC     parse.o
parse.c: In function 'msg2ct':
parse.c:258:34: error: 'NULL' undeclared (first use in this function)
parse.c:258:34: note: each undeclared identifier is reported only once for each function it appears in
parse.c: In function 'msg2exp':
parse.c:438:16: error: 'NULL' undeclared (first use in this function)

---
 src/parse.c |    1 +
 1 file changed, 1 insertion(+)

Index: conntrack-tools/src/parse.c
===================================================================
--- conntrack-tools.orig/src/parse.c
+++ conntrack-tools/src/parse.c
@@ -17,6 +17,7 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include <stdio.h>
 #include "network.h"
 
 #include <libnetfilter_conntrack/libnetfilter_conntrack.h>