diff --git a/libraries/chain/controller.cpp b/libraries/chain/controller.cpp
index 75aae0eabe..600251aaa1 100644
--- a/libraries/chain/controller.cpp
+++ b/libraries/chain/controller.cpp
@@ -811,7 +811,7 @@ struct controller_impl {
    chainbase::database             db;
    block_log                       blog;
    std::optional<pending_state>    pending;
-   mutable fork_database           fork_db;
+   fork_database                   fork_db;
    std::optional<chain_pacemaker>  pacemaker;
    std::atomic<uint32_t>           if_irreversible_block_num{0};
    resource_limits_manager         resource_limits;
diff --git a/libraries/chain/include/eosio/chain/fork_database.hpp b/libraries/chain/include/eosio/chain/fork_database.hpp
index 654b583095..9e90c6e310 100644
--- a/libraries/chain/include/eosio/chain/fork_database.hpp
+++ b/libraries/chain/include/eosio/chain/fork_database.hpp
@@ -133,6 +133,15 @@ namespace eosio::chain {
             return std::visit([&](auto& forkdb) -> R { return f(forkdb); }, v);
       }
 
+      template <class R, class F>
+      R apply(const F& f) const {
+         std::lock_guard g(m);
+         if constexpr (std::is_same_v<void, R>)
+            std::visit([&](const auto& forkdb) { f(forkdb); }, v);
+         else
+            return std::visit([&](const auto& forkdb) -> R { return f(forkdb); }, v);
+      }
+
       template <class R, class F>
       R apply_if(const F& f) {
          if constexpr (std::is_same_v<void, R>)