diff --git a/src/libfetchers/fetch-settings.cc b/src/libfetchers/fetch-settings.cc
index 007f2725f..b278835ad 100644
--- a/src/libfetchers/fetch-settings.cc
+++ b/src/libfetchers/fetch-settings.cc
@@ -7,6 +7,32 @@
 
 namespace nix {
 
+void to_json(nlohmann::json & j, const AcceptFlakeConfig & e)
+{
+    if (e == AcceptFlakeConfig::False) {
+        j = false;
+    } else if (e == AcceptFlakeConfig::Ask) {
+        j = "ask";
+    } else if (e == AcceptFlakeConfig::True) {
+        j = true;
+    } else {
+        abort();
+    }
+}
+
+void from_json(const nlohmann::json & j, AcceptFlakeConfig & e)
+{
+    if (j == false) {
+        e = AcceptFlakeConfig::False;
+    } else if (j == "ask") {
+        e = AcceptFlakeConfig::Ask;
+    } else if (j == true) {
+        e = AcceptFlakeConfig::True;
+    } else {
+        throw Error("Invalid accept-flake-config value '%s'", std::string(j));
+    }
+}
+
 template<> AcceptFlakeConfig BaseSetting<AcceptFlakeConfig>::parse(const std::string & str, const ApplyConfigOptions & options) const
 {
     if (str == "true") return AcceptFlakeConfig::True;
diff --git a/src/libfetchers/fetch-settings.hh b/src/libfetchers/fetch-settings.hh
index 93123463c..0bdc707ec 100644
--- a/src/libfetchers/fetch-settings.hh
+++ b/src/libfetchers/fetch-settings.hh
@@ -13,6 +13,9 @@ namespace nix {
 
 enum class AcceptFlakeConfig { False, Ask, True };
 
+void to_json(nlohmann::json & j, const AcceptFlakeConfig & e);
+void from_json(const nlohmann::json & j, AcceptFlakeConfig & e);
+
 struct FetchSettings : public Config
 {
     FetchSettings();
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index c114e22dc..ffc2543ef 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -269,11 +269,31 @@ Path Settings::getDefaultSSLCertFile()
 
 const std::string nixVersion = PACKAGE_VERSION;
 
-NLOHMANN_JSON_SERIALIZE_ENUM(SandboxMode, {
-    {SandboxMode::smEnabled, true},
-    {SandboxMode::smRelaxed, "relaxed"},
-    {SandboxMode::smDisabled, false},
-});
+void to_json(nlohmann::json & j, const SandboxMode & e)
+{
+    if (e == SandboxMode::smEnabled) {
+        j = true;
+    } else if (e == SandboxMode::smRelaxed) {
+        j = "relaxed";
+    } else if (e == SandboxMode::smDisabled) {
+        j = false;
+    } else {
+        abort();
+    }
+}
+
+void from_json(const nlohmann::json & j, SandboxMode & e)
+{
+    if (j == true) {
+        e = SandboxMode::smEnabled;
+    } else if (j == "relaxed") {
+        e = SandboxMode::smRelaxed;
+    } else if (j == false) {
+        e = SandboxMode::smDisabled;
+    } else {
+        throw Error("Invalid sandbox mode '%s'", std::string(j));
+    }
+}
 
 template<> SandboxMode BaseSetting<SandboxMode>::parse(const std::string & str, const ApplyConfigOptions & options) const
 {
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 94aa60825..bfba6ab01 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -14,6 +14,9 @@ namespace nix {
 
 typedef enum { smEnabled, smRelaxed, smDisabled } SandboxMode;
 
+void to_json(nlohmann::json & j, const SandboxMode & e);
+void from_json(const nlohmann::json & j, SandboxMode & e);
+
 struct MaxBuildJobsSetting : public BaseSetting<unsigned int>
 {
     MaxBuildJobsSetting(Config * options,