diff --git a/src/libcmd/common-eval-args.cc b/src/libcmd/common-eval-args.cc
index 865901febf4..c457a49f50b 100644
--- a/src/libcmd/common-eval-args.cc
+++ b/src/libcmd/common-eval-args.cc
@@ -19,9 +19,8 @@
 
 namespace nix {
 
-EvalSettings evalSettings{
-    settings.readOnlyMode,
-    {
+static GlobalConfig::Register rEvalSettings(&evalSettings, [] {
+    evalSettings.lookupPathHooks = {
         {
             "flake",
             [](EvalState & state, std::string_view rest) {
@@ -40,10 +39,8 @@ EvalSettings evalSettings{
                 return state.storePath(storePath);
             },
         },
-    },
-};
-
-static GlobalConfig::Register rEvalSettings(&evalSettings);
+    };
+});
 
 flake::Settings flakeSettings;
 
diff --git a/src/libexpr-c/nix_api_expr.cc b/src/libexpr-c/nix_api_expr.cc
index bfbd0a9c361..8acdecf49a9 100644
--- a/src/libexpr-c/nix_api_expr.cc
+++ b/src/libexpr-c/nix_api_expr.cc
@@ -6,6 +6,7 @@
 #include "nix/expr/eval-gc.hh"
 #include "nix/store/globals.hh"
 #include "nix/expr/eval-settings.hh"
+#include "nix/fetchers/fetch-settings.hh"
 #include "nix/util/ref.hh"
 
 #include "nix_api_expr.h"
@@ -137,8 +138,8 @@ nix_eval_state_builder * nix_eval_state_builder_new(nix_c_context * context, Sto
         return unsafe_new_with_self<nix_eval_state_builder>([&](auto * self) {
             return nix_eval_state_builder{
                 .store = nix::ref<nix::Store>(store->ptr),
-                .settings = nix::EvalSettings{/* &bool */ self->readOnlyMode},
-                .fetchSettings = nix::fetchers::Settings{},
+                .settings = &nix::evalSettings,
+                .fetchSettings = &nix::fetchSettings,
                 .readOnlyMode = true,
             };
         });
@@ -159,9 +160,9 @@ nix_err nix_eval_state_builder_load(nix_c_context * context, nix_eval_state_buil
         context->last_err_code = NIX_OK;
     try {
         // TODO: load in one go?
-        builder->settings.readOnlyMode = nix::settings.readOnlyMode;
-        loadConfFile(builder->settings);
-        loadConfFile(builder->fetchSettings);
+        builder->settings->readOnlyMode = nix::settings.readOnlyMode;
+        loadConfFile(*builder->settings);
+        loadConfFile(*builder->fetchSettings);
     }
     NIXC_CATCH_ERRS
 }
@@ -188,9 +189,9 @@ EvalState * nix_eval_state_build(nix_c_context * context, nix_eval_state_builder
     try {
         return unsafe_new_with_self<EvalState>([&](auto * self) {
             return EvalState{
-                .fetchSettings = std::move(builder->fetchSettings),
-                .settings = std::move(builder->settings),
-                .state = nix::EvalState(builder->lookupPath, builder->store, self->fetchSettings, self->settings),
+                .fetchSettings = builder->fetchSettings,
+                .settings = builder->settings,
+                .state = nix::EvalState(builder->lookupPath, builder->store, *self->fetchSettings, *self->settings),
             };
         });
     }
diff --git a/src/libexpr-c/nix_api_expr_internal.h b/src/libexpr-c/nix_api_expr_internal.h
index 07c7a2194df..150c4b93159 100644
--- a/src/libexpr-c/nix_api_expr_internal.h
+++ b/src/libexpr-c/nix_api_expr_internal.h
@@ -13,8 +13,8 @@ extern "C" {
 struct nix_eval_state_builder
 {
     nix::ref<nix::Store> store;
-    nix::EvalSettings settings;
-    nix::fetchers::Settings fetchSettings;
+    nix::EvalSettings * settings;
+    nix::fetchers::Settings * fetchSettings;
     nix::LookupPath lookupPath;
     // TODO: make an EvalSettings setting own this instead?
     bool readOnlyMode;
@@ -22,8 +22,8 @@ struct nix_eval_state_builder
 
 struct EvalState
 {
-    nix::fetchers::Settings fetchSettings;
-    nix::EvalSettings settings;
+    nix::fetchers::Settings * fetchSettings;
+    nix::EvalSettings * settings;
     nix::EvalState state;
 };
 
diff --git a/src/libexpr/eval-settings.cc b/src/libexpr/eval-settings.cc
index 27205864b8b..e38268e5f5d 100644
--- a/src/libexpr/eval-settings.cc
+++ b/src/libexpr/eval-settings.cc
@@ -1,4 +1,5 @@
 #include "nix/util/users.hh"
+#include "nix/util/config-global.hh"
 #include "nix/store/globals.hh"
 #include "nix/store/profiles.hh"
 #include "nix/expr/eval.hh"
@@ -118,4 +119,8 @@ std::filesystem::path getNixDefExpr()
     return settings.useXDGBaseDirectories ? getStateDir() / "defexpr" : getHome() / ".nix-defexpr";
 }
 
+EvalSettings evalSettings{settings.readOnlyMode};
+
+static GlobalConfig::Register rEvalSettings(&evalSettings);
+
 } // namespace nix
diff --git a/src/libexpr/include/nix/expr/eval-settings.hh b/src/libexpr/include/nix/expr/eval-settings.hh
index f367541ec2f..50c7b7d6085 100644
--- a/src/libexpr/include/nix/expr/eval-settings.hh
+++ b/src/libexpr/include/nix/expr/eval-settings.hh
@@ -412,4 +412,9 @@ std::filesystem::path getNixDefExpr();
  */
 constexpr size_t evalStackSize = 60 * 1024 * 1024;
 
+/**
+ * EvalSettings instance from libexpr.
+ */
+extern EvalSettings evalSettings;
+
 } // namespace nix
diff --git a/src/libflake-c/nix_api_flake.cc b/src/libflake-c/nix_api_flake.cc
index 793db44b438..ba7b6bd7f15 100644
--- a/src/libflake-c/nix_api_flake.cc
+++ b/src/libflake-c/nix_api_flake.cc
@@ -32,7 +32,7 @@ nix_err nix_flake_settings_add_to_eval_state_builder(
 {
     nix_clear_err(context);
     try {
-        settings->settings->configureEvalSettings(builder->settings);
+        settings->settings->configureEvalSettings(*builder->settings);
     }
     NIXC_CATCH_ERRS
 }
diff --git a/src/libutil/config-global.cc b/src/libutil/config-global.cc
index b63b4aaa1bb..2dd81f5c203 100644
--- a/src/libutil/config-global.cc
+++ b/src/libutil/config-global.cc
@@ -61,7 +61,16 @@ GlobalConfig globalConfig;
 
 GlobalConfig::Register::Register(Config * config)
 {
-    configRegistrations().emplace_back(config);
+    auto regs = configRegistrations();
+    if (std::find(regs.begin(), regs.end(), config) == regs.end()) {
+        configRegistrations().emplace_back(config);
+    }
+}
+
+GlobalConfig::Register::Register(Config * config, std::function<void()> && callback)
+    : Register(config)
+{
+    callback();
 }
 
 ExperimentalFeatureSettings experimentalFeatureSettings;
diff --git a/src/libutil/include/nix/util/config-global.hh b/src/libutil/include/nix/util/config-global.hh
index 5074351e046..de6923c1de7 100644
--- a/src/libutil/include/nix/util/config-global.hh
+++ b/src/libutil/include/nix/util/config-global.hh
@@ -26,6 +26,7 @@ struct GlobalConfig : public AbstractConfig
     struct Register
     {
         Register(Config * config);
+        Register(Config * config, std::function<void()> && callback);
     };
 };