diff --git a/src/console_cmds.cpp b/src/console_cmds.cpp
index 09a0bec421..9674f58c70 100644
--- a/src/console_cmds.cpp
+++ b/src/console_cmds.cpp
@@ -425,7 +425,7 @@ static bool ConSave(std::span<std::string_view> argv)
 		std::string filename = fmt::format("{}.sav", argv[1]);
 		IConsolePrint(CC_DEFAULT, "Saving map...");
 
-		if (SaveOrLoad(filename, SLO_SAVE, DFT_GAME_FILE, SAVE_DIR) != SL_OK) {
+		if (SaveOrLoad(filename, SLO_SAVE, DetailedFileType::GameFile, SAVE_DIR) != SL_OK) {
 			IConsolePrint(CC_ERROR, "Saving map failed.");
 		} else {
 			IConsolePrint(CC_INFO, "Map successfully saved to '{}'.", filename);
@@ -627,9 +627,9 @@ static bool ConChangeDirectory(std::span<std::string_view> argv)
 	const FiosItem *item = _console_file_list_savegame.FindItem(file);
 	if (item != nullptr) {
 		switch (item->type.detailed) {
-			case DFT_FIOS_DIR:
-			case DFT_FIOS_DRIVE:
-			case DFT_FIOS_PARENT:
+			case DetailedFileType::FiosDirectory:
+			case DetailedFileType::FiosDrive:
+			case DetailedFileType::FiosParent:
 				FiosBrowseTo(item);
 				break;
 			default: IConsolePrint(CC_ERROR, "{}: Not a directory.", file);
diff --git a/src/crashlog.cpp b/src/crashlog.cpp
index 56f0af2155..6cfdc4dd51 100644
--- a/src/crashlog.cpp
+++ b/src/crashlog.cpp
@@ -232,7 +232,7 @@ bool CrashLog::WriteSavegame()
 		this->savegame_filename = this->CreateFileName(".sav");
 
 		/* Don't do a threaded saveload. */
-		return SaveOrLoad(this->savegame_filename, SLO_SAVE, DFT_GAME_FILE, NO_DIRECTORY, false) == SL_OK;
+		return SaveOrLoad(this->savegame_filename, SLO_SAVE, DetailedFileType::GameFile, NO_DIRECTORY, false) == SL_OK;
 	} catch (...) {
 		return false;
 	}
diff --git a/src/fileio_type.h b/src/fileio_type.h
index f47eab2417..e392b3de6b 100644
--- a/src/fileio_type.h
+++ b/src/fileio_type.h
@@ -25,27 +25,27 @@ enum class AbstractFileType : uint8_t {
 };
 
 /** Kinds of files in each #AbstractFileType. */
-enum DetailedFileType : uint8_t {
+enum class DetailedFileType : uint8_t {
 	/* Save game and scenario files. */
-	DFT_OLD_GAME_FILE, ///< Old save game or scenario file.
-	DFT_GAME_FILE,     ///< Save game or scenario file.
+	OldGameFile, ///< Old save game or scenario file.
+	GameFile, ///< Save game or scenario file.
 
 	/* Heightmap files. */
-	DFT_HEIGHTMAP_BMP, ///< BMP file.
-	DFT_HEIGHTMAP_PNG, ///< PNG file.
+	HeightmapBmp, ///< BMP file.
+	HeightmapPng, ///< PNG file.
 
 	/* Town data files. */
-	DFT_TOWN_DATA_JSON,  ///< JSON file.
+	TownDataJson, ///< JSON file.
 
 	/* fios 'files' */
-	DFT_FIOS_DRIVE,  ///< A drive (letter) entry.
-	DFT_FIOS_PARENT, ///< A parent directory entry.
-	DFT_FIOS_DIR,    ///< A directory entry.
-	DFT_FIOS_DIRECT, ///< Direct filename.
+	FiosDrive, ///< A drive (letter) entry.
+	FiosParent, ///< A parent directory entry.
+	FiosDirectory, ///< A directory entry.
+	FiosDirect, ///< Direct filename.
 
-	DFT_END,         ///< End of this enum. Supports a compile time size check against _fios_colours in fios_gui.cpp
+	End, ///< End marker.
 
-	DFT_INVALID = 255, ///< Unknown or invalid file.
+	Invalid = 255, ///< Unknown or invalid file.
 };
 
 /** Operation performed on the file. */
@@ -67,20 +67,20 @@ struct FiosType {
 	constexpr bool operator==(const FiosType &) const noexcept = default;
 };
 
-constexpr FiosType FIOS_TYPE_DRIVE{AbstractFileType::None, DFT_FIOS_DRIVE};
-constexpr FiosType FIOS_TYPE_PARENT{AbstractFileType::None, DFT_FIOS_PARENT};
-constexpr FiosType FIOS_TYPE_DIR{AbstractFileType::None, DFT_FIOS_DIR};
-constexpr FiosType FIOS_TYPE_DIRECT{AbstractFileType::None, DFT_FIOS_DIRECT};
+constexpr FiosType FIOS_TYPE_DRIVE{AbstractFileType::None, DetailedFileType::FiosDrive};
+constexpr FiosType FIOS_TYPE_PARENT{AbstractFileType::None, DetailedFileType::FiosParent};
+constexpr FiosType FIOS_TYPE_DIR{AbstractFileType::None, DetailedFileType::FiosDirectory};
+constexpr FiosType FIOS_TYPE_DIRECT{AbstractFileType::None, DetailedFileType::FiosDirect};
 
-constexpr FiosType FIOS_TYPE_FILE{AbstractFileType::Savegame, DFT_GAME_FILE};
-constexpr FiosType FIOS_TYPE_OLDFILE{AbstractFileType::Savegame, DFT_OLD_GAME_FILE};
-constexpr FiosType FIOS_TYPE_SCENARIO{AbstractFileType::Scenario, DFT_GAME_FILE};
-constexpr FiosType FIOS_TYPE_OLD_SCENARIO{AbstractFileType::Scenario, DFT_OLD_GAME_FILE};
-constexpr FiosType FIOS_TYPE_PNG{AbstractFileType::Heightmap, DFT_HEIGHTMAP_PNG};
-constexpr FiosType FIOS_TYPE_BMP{AbstractFileType::Heightmap, DFT_HEIGHTMAP_BMP};
-constexpr FiosType FIOS_TYPE_JSON{AbstractFileType::TownData, DFT_TOWN_DATA_JSON};
+constexpr FiosType FIOS_TYPE_FILE{AbstractFileType::Savegame, DetailedFileType::GameFile};
+constexpr FiosType FIOS_TYPE_OLDFILE{AbstractFileType::Savegame, DetailedFileType::OldGameFile};
+constexpr FiosType FIOS_TYPE_SCENARIO{AbstractFileType::Scenario, DetailedFileType::GameFile};
+constexpr FiosType FIOS_TYPE_OLD_SCENARIO{AbstractFileType::Scenario, DetailedFileType::OldGameFile};
+constexpr FiosType FIOS_TYPE_PNG{AbstractFileType::Heightmap, DetailedFileType::HeightmapPng};
+constexpr FiosType FIOS_TYPE_BMP{AbstractFileType::Heightmap, DetailedFileType::HeightmapBmp};
+constexpr FiosType FIOS_TYPE_JSON{AbstractFileType::TownData, DetailedFileType::TownDataJson};
 
-constexpr FiosType FIOS_TYPE_INVALID{AbstractFileType::Invalid, DFT_INVALID};
+constexpr FiosType FIOS_TYPE_INVALID{AbstractFileType::Invalid, DetailedFileType::Invalid};
 
 /**
  * The different kinds of subdirectories OpenTTD uses
diff --git a/src/fios.cpp b/src/fios.cpp
index 06513ed114..64073f7a4b 100644
--- a/src/fios.cpp
+++ b/src/fios.cpp
@@ -133,17 +133,17 @@ std::string FiosGetCurrentPath()
 bool FiosBrowseTo(const FiosItem *item)
 {
 	switch (item->type.detailed) {
-		case DFT_FIOS_DRIVE:
+		case DetailedFileType::FiosDrive:
 #if defined(_WIN32)
 			assert(_fios_path != nullptr);
 			*_fios_path = std::string{ item->name, 0, 1 } + ":" PATHSEP;
 #endif
 			break;
 
-		case DFT_INVALID:
+		case DetailedFileType::Invalid:
 			break;
 
-		case DFT_FIOS_PARENT: {
+		case DetailedFileType::FiosParent: {
 			assert(_fios_path != nullptr);
 			auto s = _fios_path->find_last_of(PATHSEPCHAR);
 			if (s != std::string::npos && s != 0) {
@@ -157,13 +157,13 @@ bool FiosBrowseTo(const FiosItem *item)
 			break;
 		}
 
-		case DFT_FIOS_DIR:
+		case DetailedFileType::FiosDirectory:
 			assert(_fios_path != nullptr);
 			*_fios_path += item->name;
 			*_fios_path += PATHSEP;
 			break;
 
-		case DFT_FIOS_DIRECT:
+		case DetailedFileType::FiosDirect:
 			assert(_fios_path != nullptr);
 			*_fios_path = item->name;
 			break;
diff --git a/src/fios_gui.cpp b/src/fios_gui.cpp
index 64abe873a8..d96ab53382 100644
--- a/src/fios_gui.cpp
+++ b/src/fios_gui.cpp
@@ -303,19 +303,17 @@ static constexpr std::initializer_list<NWidgetPart> _nested_save_dialog_widgets
 };
 
 /** Text colours of #DetailedFileType fios entries in the window. */
-static const TextColour _fios_colours[] = {
-	TC_LIGHT_BROWN,  // DFT_OLD_GAME_FILE
-	TC_ORANGE,       // DFT_GAME_FILE
-	TC_YELLOW,       // DFT_HEIGHTMAP_BMP
-	TC_ORANGE,       // DFT_HEIGHTMAP_PNG
-	TC_LIGHT_BROWN,  // DFT_TOWN_DATA_JSON
-	TC_LIGHT_BLUE,   // DFT_FIOS_DRIVE
-	TC_DARK_GREEN,   // DFT_FIOS_PARENT
-	TC_DARK_GREEN,   // DFT_FIOS_DIR
-	TC_ORANGE,       // DFT_FIOS_DIRECT
+static const EnumClassIndexContainer<std::array<TextColour, to_underlying(DetailedFileType::End)>, DetailedFileType> _fios_colours = {
+	TC_LIGHT_BROWN, // DetailedFileType::OldGameFile
+	TC_ORANGE, // DetailedFileType::GameFile
+	TC_YELLOW, // DetailedFileType::HeightmapBmp
+	TC_ORANGE, // DetailedFileType::HeightmapPng
+	TC_LIGHT_BROWN, // DetailedFileType::TownDataJson
+	TC_LIGHT_BLUE, // DetailedFileType::FiosDrive
+	TC_DARK_GREEN, // DetailedFileType::FiosParent
+	TC_DARK_GREEN, // DetailedFileType::FiosDirectory
+	TC_ORANGE, // DetailedFileType::FiosDirect
 };
-/* This should align with the DetailedFileType enum defined in fileio_type.h */
-static_assert(std::size(_fios_colours) == DFT_END);
 
 /**
  * Sort the collected list save games prior to displaying it in the save/load gui.
@@ -332,9 +330,9 @@ static void SortSaveGameList(FileList &file_list)
 	 */
 	for (const auto &item : file_list) {
 		switch (item.type.detailed) {
-			case DFT_FIOS_DIR:    sort_start++; break;
-			case DFT_FIOS_PARENT: sort_start++; break;
-			case DFT_FIOS_DRIVE:  sort_end++;   break;
+			case DetailedFileType::FiosDirectory: sort_start++; break;
+			case DetailedFileType::FiosParent: sort_start++; break;
+			case DetailedFileType::FiosDrive: sort_end++; break;
 			default: break;
 		}
 	}
@@ -759,9 +757,9 @@ public:
 						this->selected = file;
 						_load_check_data.Clear();
 
-						if (file->type.detailed == DFT_GAME_FILE) {
+						if (file->type.detailed == DetailedFileType::GameFile) {
 							/* Other detailed file types cannot be checked before. */
-							SaveOrLoad(file->name, SLO_CHECK, DFT_GAME_FILE, NO_DIRECTORY, false);
+							SaveOrLoad(file->name, SLO_CHECK, DetailedFileType::GameFile, NO_DIRECTORY, false);
 						}
 
 						this->InvalidateData(SLIWD_SELECTION_CHANGES);
diff --git a/src/genworld.cpp b/src/genworld.cpp
index 596d8683b0..a381a2c5b1 100644
--- a/src/genworld.cpp
+++ b/src/genworld.cpp
@@ -217,7 +217,7 @@ static void _GenerateWorld()
 
 		if (_debug_desync_level > 0) {
 			std::string name = fmt::format("dmp_cmds_{:08x}_{:08x}.sav", _settings_game.game_creation.generation_seed, TimerGameEconomy::date);
-			SaveOrLoad(name, SLO_SAVE, DFT_GAME_FILE, AUTOSAVE_DIR, false);
+			SaveOrLoad(name, SLO_SAVE, DetailedFileType::GameFile, AUTOSAVE_DIR, false);
 		}
 	} catch (AbortGenerateWorldSignal&) {
 		CleanupGeneration();
diff --git a/src/heightmap.cpp b/src/heightmap.cpp
index ae0c193454..1c4c141df4 100644
--- a/src/heightmap.cpp
+++ b/src/heightmap.cpp
@@ -505,11 +505,11 @@ static bool ReadHeightMap(DetailedFileType dft, std::string_view filename, uint
 			NOT_REACHED();
 
 #ifdef WITH_PNG
-		case DFT_HEIGHTMAP_PNG:
+		case DetailedFileType::HeightmapPng:
 			return ReadHeightmapPNG(filename, x, y, map);
 #endif /* WITH_PNG */
 
-		case DFT_HEIGHTMAP_BMP:
+		case DetailedFileType::HeightmapBmp:
 			return ReadHeightmapBMP(filename, x, y, map);
 	}
 }
diff --git a/src/network/network_client.cpp b/src/network/network_client.cpp
index eba5eed713..eb61867e20 100644
--- a/src/network/network_client.cpp
+++ b/src/network/network_client.cpp
@@ -863,7 +863,7 @@ NetworkRecvStatus ClientNetworkGameSocketHandler::Receive_SERVER_MAP_DONE(Packet
 	/* Set the abstract filetype. This is read during savegame load. */
 	_file_to_saveload.SetMode(FIOS_TYPE_FILE, SLO_LOAD);
 
-	bool load_success = SafeLoad({}, SLO_LOAD, DFT_GAME_FILE, GM_NORMAL, NO_DIRECTORY, this->savegame);
+	bool load_success = SafeLoad({}, SLO_LOAD, DetailedFileType::GameFile, GM_NORMAL, NO_DIRECTORY, this->savegame);
 	this->savegame = nullptr;
 
 	/* Long savegame loads shouldn't affect the lag calculation! */
diff --git a/src/openttd.cpp b/src/openttd.cpp
index 96351e5dd3..ff93f9d6a0 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -329,7 +329,7 @@ static void LoadIntroGame(bool load_newgrfs = true)
 	SetupColoursAndInitialWindow();
 
 	/* Load the default opening screen savegame */
-	if (SaveOrLoad("opntitle.dat", SLO_LOAD, DFT_GAME_FILE, BASESET_DIR) != SL_OK) {
+	if (SaveOrLoad("opntitle.dat", SLO_LOAD, DetailedFileType::GameFile, BASESET_DIR) != SL_OK) {
 		GenerateWorld(GWM_EMPTY, 64, 64); // if failed loading, make empty world.
 		SetLocalCompany(COMPANY_SPECTATOR);
 	} else {
@@ -612,7 +612,7 @@ int openttd_main(std::span<std::string_view> arguments)
 			auto [_, title] = FiosGetSavegameListCallback(SLO_LOAD, mgo.opt, extension);
 
 			_load_check_data.Clear();
-			SaveOrLoadResult res = SaveOrLoad(mgo.opt, SLO_CHECK, DFT_GAME_FILE, SAVE_DIR, false);
+			SaveOrLoadResult res = SaveOrLoad(mgo.opt, SLO_CHECK, DetailedFileType::GameFile, SAVE_DIR, false);
 			if (res != SL_OK || _load_check_data.HasErrors()) {
 				fmt::print(stderr, "Failed to open savegame\n");
 				if (_load_check_data.HasErrors()) {
@@ -939,7 +939,7 @@ static void MakeNewEditorWorld()
 bool SafeLoad(const std::string &filename, SaveLoadOperation fop, DetailedFileType dft, GameMode newgm, Subdirectory subdir, std::shared_ptr<LoadFilter> lf = nullptr)
 {
 	assert(fop == SLO_LOAD);
-	assert(dft == DFT_GAME_FILE || (lf == nullptr && dft == DFT_OLD_GAME_FILE));
+	assert(dft == DetailedFileType::GameFile || (lf == nullptr && dft == DetailedFileType::OldGameFile));
 	GameMode ogm = _game_mode;
 
 	_game_mode = newgm;
@@ -1175,7 +1175,7 @@ void SwitchToMode(SwitchMode new_mode)
 
 		case SM_SAVE_GAME: // Save game.
 			/* Make network saved games on pause compatible to singleplayer mode */
-			if (SaveOrLoad(_file_to_saveload.name, SLO_SAVE, DFT_GAME_FILE, NO_DIRECTORY) != SL_OK) {
+			if (SaveOrLoad(_file_to_saveload.name, SLO_SAVE, DetailedFileType::GameFile, NO_DIRECTORY) != SL_OK) {
 				ShowErrorMessage(GetSaveLoadErrorType(), GetSaveLoadErrorMessage(), WL_ERROR);
 			} else {
 				CloseWindowById(WC_SAVELOAD, 0);
@@ -1245,7 +1245,7 @@ void StateGameLoop()
 		if (_debug_desync_level > 2 && TimerGameEconomy::date_fract == 0 && (TimerGameEconomy::date.base() & 0x1F) == 0) {
 			/* Save the desync savegame if needed. */
 			std::string name = fmt::format("dmp_cmds_{:08x}_{:08x}.sav", _settings_game.game_creation.generation_seed, TimerGameEconomy::date);
-			SaveOrLoad(name, SLO_SAVE, DFT_GAME_FILE, AUTOSAVE_DIR, false);
+			SaveOrLoad(name, SLO_SAVE, DetailedFileType::GameFile, AUTOSAVE_DIR, false);
 		}
 
 		CheckCaches();
diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
index 9114cc118e..efbfbb8328 100644
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -3293,7 +3293,7 @@ SaveOrLoadResult LoadWithFilter(std::shared_ptr<LoadFilter> reader)
 SaveOrLoadResult SaveOrLoad(std::string_view filename, SaveLoadOperation fop, DetailedFileType dft, Subdirectory sb, bool threaded)
 {
 	/* An instance of saving is already active, so don't go saving again */
-	if (_sl.saveinprogress && fop == SLO_SAVE && dft == DFT_GAME_FILE && threaded) {
+	if (_sl.saveinprogress && fop == SLO_SAVE && dft == DetailedFileType::GameFile && threaded) {
 		/* if not an autosave, but a user action, show error message */
 		if (!_do_autosave) ShowErrorMessage(GetEncodedString(STR_ERROR_SAVE_STILL_IN_PROGRESS), {}, WL_ERROR);
 		return SL_OK;
@@ -3302,7 +3302,7 @@ SaveOrLoadResult SaveOrLoad(std::string_view filename, SaveLoadOperation fop, De
 
 	try {
 		/* Load a TTDLX or TTDPatch game */
-		if (fop == SLO_LOAD && dft == DFT_OLD_GAME_FILE) {
+		if (fop == SLO_LOAD && dft == DetailedFileType::OldGameFile) {
 			ResetSaveloadData();
 
 			InitializeGame(256, 256, true, true); // set a mapsize of 256x256 for TTDPatch games or it might get confused
@@ -3325,7 +3325,7 @@ SaveOrLoadResult SaveOrLoad(std::string_view filename, SaveLoadOperation fop, De
 			return SL_OK;
 		}
 
-		assert(dft == DFT_GAME_FILE);
+		assert(dft == DetailedFileType::GameFile);
 		switch (fop) {
 			case SLO_CHECK:
 				_sl.action = SLA_LOAD_CHECK;
@@ -3391,7 +3391,7 @@ void DoAutoOrNetsave(FiosNumberedSaveName &counter)
 	}
 
 	Debug(sl, 2, "Autosaving to '{}'", filename);
-	if (SaveOrLoad(filename, SLO_SAVE, DFT_GAME_FILE, AUTOSAVE_DIR) != SL_OK) {
+	if (SaveOrLoad(filename, SLO_SAVE, DetailedFileType::GameFile, AUTOSAVE_DIR) != SL_OK) {
 		ShowErrorMessage(GetEncodedString(STR_ERROR_AUTOSAVE_FAILED), {}, WL_ERROR);
 	}
 }
@@ -3400,7 +3400,7 @@ void DoAutoOrNetsave(FiosNumberedSaveName &counter)
 /** Do a save when exiting the game (_settings_client.gui.autosave_on_exit) */
 void DoExitSave()
 {
-	SaveOrLoad("exit.sav", SLO_SAVE, DFT_GAME_FILE, AUTOSAVE_DIR);
+	SaveOrLoad("exit.sav", SLO_SAVE, DetailedFileType::GameFile, AUTOSAVE_DIR);
 }
 
 /**