diff --git a/examples/dns.c b/examples/dns.c
index ce1e9ed..f3903c4 100644
--- a/examples/dns.c
+++ b/examples/dns.c
@@ -1,5 +1,6 @@
 #include "../src/hammer.h"
 #include "dns_common.h"
+#include "dns.h"
 
 #define false 0
 #define true 1
@@ -32,6 +33,8 @@ bool validate_dns(parse_result_t *p) {
   return true;
 }
 
+const parsed_token_t* pack_dns_struct(const parse_result_t *p);
+
 const parser_t* init_parser() {
   static parser_t *dns_message = NULL;
   if (dns_message)
diff --git a/src/hammer.c b/src/hammer.c
index 19d2db2..55a2fdc 100644
--- a/src/hammer.c
+++ b/src/hammer.c
@@ -1123,7 +1123,7 @@ static void test_whitespace(void) {
 
 #include <ctype.h>
 
-const parsed_token_t* upcase(parse_result_t *p) {
+const parsed_token_t* upcase(const parse_result_t *p) {
   switch(p->ast->token_type) {
   case TT_SEQUENCE:
     {
diff --git a/src/hammer.h b/src/hammer.h
index b3bd412..b724773 100644
--- a/src/hammer.h
+++ b/src/hammer.h
@@ -90,7 +90,7 @@ typedef struct parse_result {
  * say, structs) and stuff values for them into the void* in the 
  * tagged union in parsed_token_t. 
  */
-typedef const parsed_token_t* (*action_t)(parse_result_t *p);
+typedef const parsed_token_t* (*action_t)(const parse_result_t *p);
 
 /**
  * Type of a boolean attribute-checking function, used in the