diff --git a/plugins/experimental/maxmind_acl/mmdb.h b/plugins/experimental/maxmind_acl/mmdb.h
index 828ffe3bff9..561b42f494c 100644
--- a/plugins/experimental/maxmind_acl/mmdb.h
+++ b/plugins/experimental/maxmind_acl/mmdb.h
@@ -104,5 +104,5 @@ class Acl
   void loadhtml(YAML::Node htmlNode);
   bool eval_country(MMDB_entry_data_s *entry_data, const char *path, int path_len);
   void parseregex(YAML::Node regex, bool allow);
-  ipstate eval_ip(const sockaddr *sock);
+  ipstate eval_ip(const sockaddr *sock) const;
 };