diff --git a/include/pkt_null.hrl b/include/pkt_null.hrl
index 6c03784..2c3b64c 100644
--- a/include/pkt_null.hrl
+++ b/include/pkt_null.hrl
@@ -1,3 +1,3 @@
 -record(null, {
-        family = ?PF_INET
+        family = ?PF_INET :: pkt:uint32_t()
     }).