diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index 98cfb932c5b..ff7e763c262 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -32,93 +32,78 @@ namespace gui2
 {
 namespace
 {
-class theme_parser
+config read_and_validate(const std::string& path)
+try {
+	preproc_map defines;
+	schema_validation::schema_validator validator{filesystem::get_wml_location("schema/gui.cfg").value()};
+	filesystem::scoped_istream stream = preprocess_file(path, &defines);
+	return ::read(*stream, &validator);
+
+} catch(const utils::bad_optional_access&) {
+	FAIL("GUI2: schema/gui.cfg not found.");
+
+} catch(const abstract_validator::error& e) {
+	FAIL("GUI2: could not read schema file: " + e.message);
+
+} catch(const config::error& e) {
+	ERR_GUI_P << "Could not read gui file: " << path;
+	ERR_GUI_P << e.what();
+	return {};
+}
+
+/**
+ * Adds a theme definition object to the global registry.
+ *
+ * @param def         A valid gui_definition config.
+ *
+ * @returns           An optional iterator to the newly-constructed definition.
+ *                    If gui_definition throws wml_exception or a theme with the
+ *                    given ID already exists, returns nullopt.
+ */
+auto register_theme(const config& def) -> utils::optional<gui_theme_map_t::iterator>
+try {
+	auto [iter, is_unique] = guis.try_emplace(def["id"], def);
+	if(is_unique) return iter;
+
+	ERR_GUI_P << "UI Theme '" << def["id"] << "' already exists.";
+	return utils::nullopt;
+
+} catch(const wml_exception& e) {
+	ERR_GUI_P << "Invalid UI theme: " << def["id"];
+	ERR_GUI_P << e.user_message;
+	return utils::nullopt;
+}
+
+/**
+ * Parses any GUI2 theme definitions at the file path specified.
+ *
+ * @param full_path   Path to file containing one or more [gui] tags.
+ * @param is_core     If true, look for the default theme here.
+ */
+void parse(const std::string& full_path, bool is_core)
 {
-public:
-	theme_parser()
-	try
-		: validator_(filesystem::get_wml_location("schema/gui.cfg").value())
-		, defines_(game_config::config_cache::instance().get_preproc_map())
-	{
-		guis.clear(); // Reset in case we're re-initializing the UI subsystem
-	} catch(const utils::bad_optional_access&) {
-		FAIL("GUI2: schema/gui.cfg not found.");
-	} catch(const abstract_validator::error& e) {
-		FAIL("GUI2: could not read schema file: " + e.message);
-	}
-
-	/**
-	 * Parses any GUI2 theme definitions at the file path specified.
-	 *
-	 * @param full_path   Path to file containing one or more [gui] tags.
-	 * @param is_core     If true, look for the default theme here.
-	 */
-	void parse(const std::string& full_path, bool is_core)
-	{
 #if __cpp_range_based_for >= 202211L // lifetime extension of temporaries
-		for(const config& def : read_and_validate(full_path).child_range("gui")) {
+	for(const config& def : read_and_validate(full_path).child_range("gui")) {
 #else
-		config cfg = read_and_validate(full_path);
-		for(const config& def : cfg.child_range("gui")) {
+	config cfg = read_and_validate(full_path);
+	for(const config& def : cfg.child_range("gui")) {
 #endif
-			const bool is_default = def["id"] == "default";
+		const bool is_default = def["id"] == "default";
 
-			if(is_default && !is_core) {
-				ERR_GUI_P << "UI theme id 'default' is reserved for core themes.";
-				continue;
-			}
+		if(is_default && !is_core) {
+			ERR_GUI_P << "UI theme id 'default' is reserved for core themes.";
+			continue;
+		}
 
-			const auto iter = register_theme(def);
-			if(!iter) continue;
+		const auto iter = register_theme(def);
+		if(!iter) continue;
 
-			if(is_default && is_core) {
-				default_gui = *iter;
-				current_gui = default_gui;
-			}
+		if(is_default && is_core) {
+			default_gui = *iter;
+			current_gui = default_gui;
 		}
 	}
-
-private:
-	auto read_and_validate(const std::string& path) -> config
-	try {
-		filesystem::scoped_istream stream = preprocess_file(path, &defines_);
-		return ::read(*stream, &validator_);
-
-	} catch(const config::error& e) {
-		ERR_GUI_P << "Could not read gui file: " << path;
-		ERR_GUI_P << e.what();
-		return {};
-	};
-
-	/**
-	 * Adds a theme definition object to the global registry.
-	 *
-	 * @param def         A valid gui_definition config.
-	 *
-	 * @returns           An optional iterator to the newly-constructed definition.
-	 *                    If errors occurred while parsing the config or a theme with
-	 *                    the given ID already exists, returns nullopt.
-	 */
-	auto register_theme(const config& def) const -> utils::optional<gui_theme_map_t::iterator>
-	try {
-		auto [iter, is_unique] = guis.try_emplace(def["id"], def);
-		if(is_unique) return iter;
-
-		ERR_GUI_P << "UI Theme '" << def["id"] << "' already exists.";
-		return utils::nullopt;
-
-	} catch(const wml_exception& e) {
-		ERR_GUI_P << "Invalid UI theme: " << def["id"];
-		ERR_GUI_P << e.user_message;
-		return utils::nullopt;
-	}
-
-	/** GUI2 schema validator. */
-	schema_validation::schema_validator validator_;
-
-	/** Common macro context shared by all themes (@todo: document this fact). */
-	preproc_map defines_;
-};
+}
 
 } // namespace
 
@@ -126,6 +111,9 @@ void init()
 {
 	LOG_GUI_G << "Initializing UI subststem.";
 
+	// Reset the registry in case we're re-initializing
+	guis.clear();
+
 	// Save current screen size.
 	settings::update_screen_size_variables();
 
@@ -133,10 +121,8 @@ void init()
 	// Parse GUI definitions from mainline
 	//
 
-	theme_parser parser;
-
 	try {
-		parser.parse(filesystem::get_wml_location("gui/_main.cfg").value(), true);
+		parse(filesystem::get_wml_location("gui/_main.cfg").value(), true);
 	} catch(const utils::bad_optional_access&) {
 		FAIL("GUI2: gui/_main.cfg not found.");
 	}
@@ -157,7 +143,7 @@ void init()
 		const std::string gui_file = umc + "/gui-theme.cfg";
 
 		if(filesystem::file_exists(gui_file)) {
-			parser.parse(gui_file, false);
+			parse(gui_file, false);
 		}
 	}
 }