diff --git a/src/fileio.cpp b/src/fileio.cpp
index 990510d545..29927236d5 100644
--- a/src/fileio.cpp
+++ b/src/fileio.cpp
@@ -1061,17 +1061,17 @@ void DeterminePaths(const char *exe, bool only_local_path)
 
 /**
  * Sanitizes a filename, i.e. removes all illegal characters from it.
- * @param filename the "\0" terminated filename
+ * @param filename the filename
  */
-void SanitizeFilename(char *filename)
+void SanitizeFilename(std::string &filename)
 {
-	for (; *filename != '\0'; filename++) {
-		switch (*filename) {
+	for (auto &c : filename) {
+		switch (c) {
 			/* The following characters are not allowed in filenames
 			 * on at least one of the supported operating systems: */
 			case ':': case '\\': case '*': case '?': case '/':
 			case '<': case '>': case '|': case '"':
-				*filename = '_';
+				c = '_';
 				break;
 		}
 	}
diff --git a/src/fileio_func.h b/src/fileio_func.h
index 7023460878..0ec0ab640c 100644
--- a/src/fileio_func.h
+++ b/src/fileio_func.h
@@ -23,7 +23,7 @@ void FioCreateDirectory(const std::string &name);
 
 const char *FiosGetScreenshotDir();
 
-void SanitizeFilename(char *filename);
+void SanitizeFilename(std::string &filename);
 void AppendPathSeparator(std::string &buf);
 void DeterminePaths(const char *exe, bool only_local_path);
 std::unique_ptr<char[]> ReadFileToMem(const std::string &filename, size_t &lenp, size_t maxsize);
diff --git a/src/fios_gui.cpp b/src/fios_gui.cpp
index 2cde115cf6..05b397f2b6 100644
--- a/src/fios_gui.cpp
+++ b/src/fios_gui.cpp
@@ -299,8 +299,7 @@ public:
 	/** Generate a default save filename. */
 	void GenerateFileName()
 	{
-		GenerateDefaultSaveName(this->filename_editbox.text.buf, &this->filename_editbox.text.buf[this->filename_editbox.text.max_bytes - 1]);
-		this->filename_editbox.text.UpdateSize();
+		this->filename_editbox.text.Assign(GenerateDefaultSaveName());
 	}
 
 	SaveLoadWindow(WindowDesc *desc, AbstractFileType abstract_filetype, SaveLoadOperation fop)
diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
index b2b626386f..39ea3f7b92 100644
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -3170,17 +3170,16 @@ SaveOrLoadResult SaveOrLoad(const std::string &filename, SaveLoadOperation fop,
  */
 void DoAutoOrNetsave(FiosNumberedSaveName &counter)
 {
-	char buf[MAX_PATH];
+	std::string filename;
 
 	if (_settings_client.gui.keep_all_autosave) {
-		GenerateDefaultSaveName(buf, lastof(buf));
-		strecat(buf, counter.Extension().c_str(), lastof(buf));
+		filename = GenerateDefaultSaveName() + counter.Extension();
 	} else {
-		strecpy(buf, counter.Filename().c_str(), lastof(buf));
+		filename = counter.Filename();
 	}
 
-	Debug(sl, 2, "Autosaving to '{}'", buf);
-	if (SaveOrLoad(buf, SLO_SAVE, DFT_GAME_FILE, AUTOSAVE_DIR) != SL_OK) {
+	Debug(sl, 2, "Autosaving to '{}'", filename);
+	if (SaveOrLoad(filename, SLO_SAVE, DFT_GAME_FILE, AUTOSAVE_DIR) != SL_OK) {
 		ShowErrorMessage(STR_ERROR_AUTOSAVE_FAILED, INVALID_STRING_ID, WL_ERROR);
 	}
 }
@@ -3193,11 +3192,9 @@ void DoExitSave()
 }
 
 /**
- * Fill the buffer with the default name for a savegame *or* screenshot.
- * @param buf the buffer to write to.
- * @param last the last element in the buffer.
+ * Get the default name for a savegame *or* screenshot.
  */
-void GenerateDefaultSaveName(char *buf, const char *last)
+std::string GenerateDefaultSaveName()
 {
 	/* Check if we have a name for this map, which is the name of the first
 	 * available company. When there's no company available we'll use
@@ -3222,8 +3219,9 @@ void GenerateDefaultSaveName(char *buf, const char *last)
 	SetDParam(2, TimerGameCalendar::date);
 
 	/* Get the correct string (special string for when there's not company) */
-	GetString(buf, !Company::IsValidID(cid) ? STR_SAVEGAME_NAME_SPECTATOR : STR_SAVEGAME_NAME_DEFAULT, last);
-	SanitizeFilename(buf);
+	std::string filename = GetString(!Company::IsValidID(cid) ? STR_SAVEGAME_NAME_SPECTATOR : STR_SAVEGAME_NAME_DEFAULT);
+	SanitizeFilename(filename);
+	return filename;
 }
 
 /**
diff --git a/src/saveload/saveload.h b/src/saveload/saveload.h
index 88fcf0602c..f1f29dace2 100644
--- a/src/saveload/saveload.h
+++ b/src/saveload/saveload.h
@@ -393,7 +393,7 @@ enum SavegameType {
 
 extern FileToSaveLoad _file_to_saveload;
 
-void GenerateDefaultSaveName(char *buf, const char *last);
+std::string GenerateDefaultSaveName();
 void SetSaveLoadError(StringID str);
 const char *GetSaveLoadErrorString();
 SaveOrLoadResult SaveOrLoad(const std::string &filename, SaveLoadOperation fop, DetailedFileType dft, Subdirectory sb, bool threaded = true);
diff --git a/src/screenshot.cpp b/src/screenshot.cpp
index 8d853c52dc..5de7f98e53 100644
--- a/src/screenshot.cpp
+++ b/src/screenshot.cpp
@@ -674,7 +674,7 @@ static const char *MakeScreenshotName(const char *default_fn, const char *ext, b
 		if (_game_mode == GM_EDITOR || _game_mode == GM_MENU || _local_company == COMPANY_SPECTATOR) {
 			strecpy(_screenshot_name, default_fn, lastof(_screenshot_name));
 		} else {
-			GenerateDefaultSaveName(_screenshot_name, lastof(_screenshot_name));
+			strecpy(_screenshot_name, GenerateDefaultSaveName().c_str(), lastof(_screenshot_name));
 		}
 	}