diff --git a/proto/aggregator/aggregator.c b/proto/aggregator/aggregator.c
index f81f5f24..deeec401 100644
--- a/proto/aggregator/aggregator.c
+++ b/proto/aggregator/aggregator.c
@@ -164,7 +164,7 @@ trie_insert_prefix(const union net_addr_union *addr, struct trie_node * const ro
 /*
  * Return first non-null bucket of the closest ancestor of @node
  */
-static struct aggregator_bucket *
+static const struct aggregator_bucket *
 get_ancestor_bucket(const struct trie_node *node)
 {
   /* Defined for other than root nodes */
diff --git a/proto/aggregator/aggregator.h b/proto/aggregator/aggregator.h
index 22638ac2..79a91ed9 100644
--- a/proto/aggregator/aggregator.h
+++ b/proto/aggregator/aggregator.h
@@ -94,8 +94,8 @@ struct aggr_item_node {
 struct trie_node {
   struct trie_node *parent;
   struct trie_node *child[2];
-  struct aggregator_bucket *bucket;
-  struct aggregator_bucket *potential_buckets[MAX_POTENTIAL_BUCKETS_COUNT];
+  const struct aggregator_bucket *bucket;
+  const struct aggregator_bucket *potential_buckets[MAX_POTENTIAL_BUCKETS_COUNT];
   int potential_buckets_count;
 };