diff --git a/trie/trie.h b/trie/trie.h
index d16407f..a1ee93e 100644
--- a/trie/trie.h
+++ b/trie/trie.h
@@ -18,7 +18,7 @@ union ipv6 {
 struct trie_node {
     struct trie_node*   _l;
     struct trie_node*   _r;
-    int           _rule:31;
+    unsigned      _rule:16;
     unsigned _rule_valid:1;
 };