diff --git a/src/fileio.cpp b/src/fileio.cpp
index b7226f5cc4..da49f47e53 100644
--- a/src/fileio.cpp
+++ b/src/fileio.cpp
@@ -344,30 +344,30 @@ void FioFCloseFile(FILE *f)
 	fclose(f);
 }
 
-char *FioGetFullPath(char *buf, size_t buflen, Searchpath sp, Subdirectory subdir, const char *filename)
+char *FioGetFullPath(char *buf, const char *last, Searchpath sp, Subdirectory subdir, const char *filename)
 {
 	assert(subdir < NUM_SUBDIRS);
 	assert(sp < NUM_SEARCHPATHS);
 
-	snprintf(buf, buflen, "%s%s%s", _searchpaths[sp], _subdirs[subdir], filename);
+	seprintf(buf, last, "%s%s%s", _searchpaths[sp], _subdirs[subdir], filename);
 	return buf;
 }
 
 /**
  * Find a path to the filename in one of the search directories.
  * @param buf [out] Destination buffer for the path.
- * @param buflen Length of the destination buffer.
+ * @param last End of the destination buffer.
  * @param subdir Subdirectory to try.
  * @param filename Filename to look for.
  * @return \a buf containing the path if the path was found, else \c NULL.
  */
-char *FioFindFullPath(char *buf, size_t buflen, Subdirectory subdir, const char *filename)
+char *FioFindFullPath(char *buf, const char *last, Subdirectory subdir, const char *filename)
 {
 	Searchpath sp;
 	assert(subdir < NUM_SUBDIRS);
 
 	FOR_ALL_SEARCHPATHS(sp) {
-		FioGetFullPath(buf, buflen, sp, subdir, filename);
+		FioGetFullPath(buf, last, sp, subdir, filename);
 		if (FileExists(buf)) return buf;
 #if !defined(WIN32)
 		/* Be, as opening files, aware that sometimes the filename
@@ -380,27 +380,27 @@ char *FioFindFullPath(char *buf, size_t buflen, Subdirectory subdir, const char
 	return NULL;
 }
 
-char *FioAppendDirectory(char *buf, size_t buflen, Searchpath sp, Subdirectory subdir)
+char *FioAppendDirectory(char *buf, const char *last, Searchpath sp, Subdirectory subdir)
 {
 	assert(subdir < NUM_SUBDIRS);
 	assert(sp < NUM_SEARCHPATHS);
 
-	snprintf(buf, buflen, "%s%s", _searchpaths[sp], _subdirs[subdir]);
+	seprintf(buf, last, "%s%s", _searchpaths[sp], _subdirs[subdir]);
 	return buf;
 }
 
-char *FioGetDirectory(char *buf, size_t buflen, Subdirectory subdir)
+char *FioGetDirectory(char *buf, const char *last, Subdirectory subdir)
 {
 	Searchpath sp;
 
 	/* Find and return the first valid directory */
 	FOR_ALL_SEARCHPATHS(sp) {
-		char *ret = FioAppendDirectory(buf, buflen, sp, subdir);
+		char *ret = FioAppendDirectory(buf, last, sp, subdir);
 		if (FileExists(buf)) return ret;
 	}
 
 	/* Could not find the directory, fall back to a base path */
-	strecpy(buf, _personal_dir, &buf[buflen - 1]);
+	strecpy(buf, _personal_dir, last);
 
 	return buf;
 }
@@ -421,7 +421,7 @@ static FILE *FioFOpenFileSp(const char *filename, const char *mode, Searchpath s
 	if (subdir == NO_DIRECTORY) {
 		strecpy(buf, filename, lastof(buf));
 	} else {
-		snprintf(buf, lengthof(buf), "%s%s%s", _searchpaths[sp], _subdirs[subdir], filename);
+		seprintf(buf, lastof(buf), "%s%s%s", _searchpaths[sp], _subdirs[subdir], filename);
 	}
 
 #if defined(WIN32)
@@ -566,20 +566,19 @@ static void FioCreateDirectory(const char *name)
 /**
  * Appends, if necessary, the path separator character to the end of the string.
  * It does not add the path separator to zero-sized strings.
- * @param buf    string to append the separator to
- * @param buflen the length of \a buf.
+ * @param buf  string to append the separator to
+ * @param last the last element of \a buf.
  * @return true iff the operation succeeded
  */
-bool AppendPathSeparator(char *buf, size_t buflen)
+bool AppendPathSeparator(char *buf, const char *last)
 {
 	size_t s = strlen(buf);
 
 	/* Length of string + path separator + '\0' */
 	if (s != 0 && buf[s - 1] != PATHSEPCHAR) {
-		if (s + 2 >= buflen) return false;
+		if (&buf[s] >= last) return false;
 
-		buf[s]     = PATHSEPCHAR;
-		buf[s + 1] = '\0';
+		seprintf(buf + s, last, "%c", PATHSEPCHAR);
 	}
 
 	return true;
@@ -603,10 +602,10 @@ char *BuildWithFullPath(const char *dir)
 	/* Add absolute path */
 	if (s == NULL || dest != s) {
 		if (getcwd(dest, MAX_PATH) == NULL) *dest = '\0';
-		AppendPathSeparator(dest, MAX_PATH);
+		AppendPathSeparator(dest, last);
 		strecat(dest, dir, last);
 	}
-	AppendPathSeparator(dest, MAX_PATH);
+	AppendPathSeparator(dest, last);
 
 	return dest;
 }
@@ -1073,8 +1072,8 @@ bool DoScanWorkingDirectory()
 	if (_searchpaths[SP_PERSONAL_DIR] == NULL) return true;
 
 	char tmp[MAX_PATH];
-	snprintf(tmp, lengthof(tmp), "%s%s", _searchpaths[SP_WORKING_DIR], PERSONAL_DIR);
-	AppendPathSeparator(tmp, MAX_PATH);
+	seprintf(tmp, lastof(tmp), "%s%s", _searchpaths[SP_WORKING_DIR], PERSONAL_DIR);
+	AppendPathSeparator(tmp, lastof(tmp));
 	return strcmp(tmp, _searchpaths[SP_PERSONAL_DIR]) != 0;
 }
 
@@ -1087,11 +1086,11 @@ void DetermineBasePaths(const char *exe)
 	char tmp[MAX_PATH];
 #if defined(WITH_XDG_BASEDIR) && defined(WITH_PERSONAL_DIR)
 	const char *xdg_data_home = xdgDataHome(NULL);
-	snprintf(tmp, MAX_PATH, "%s" PATHSEP "%s", xdg_data_home,
+	seprintf(tmp, lastof(tmp), "%s" PATHSEP "%s", xdg_data_home,
 			PERSONAL_DIR[0] == '.' ? &PERSONAL_DIR[1] : PERSONAL_DIR);
 	free(xdg_data_home);
 
-	AppendPathSeparator(tmp, MAX_PATH);
+	AppendPathSeparator(tmp, lastof(tmp));
 	_searchpaths[SP_PERSONAL_DIR_XDG] = strdup(tmp);
 #endif
 #if defined(__MORPHOS__) || defined(__AMIGA__) || defined(DOS) || defined(OS2) || !defined(WITH_PERSONAL_DIR)
@@ -1119,8 +1118,8 @@ void DetermineBasePaths(const char *exe)
 
 	if (homedir != NULL) {
 		ValidateString(homedir);
-		snprintf(tmp, MAX_PATH, "%s" PATHSEP "%s", homedir, PERSONAL_DIR);
-		AppendPathSeparator(tmp, MAX_PATH);
+		seprintf(tmp, lastof(tmp), "%s" PATHSEP "%s", homedir, PERSONAL_DIR);
+		AppendPathSeparator(tmp, lastof(tmp));
 
 		_searchpaths[SP_PERSONAL_DIR] = strdup(tmp);
 		free(homedir);
@@ -1130,8 +1129,8 @@ void DetermineBasePaths(const char *exe)
 #endif
 
 #if defined(WITH_SHARED_DIR)
-	snprintf(tmp, MAX_PATH, "%s", SHARED_DIR);
-	AppendPathSeparator(tmp, MAX_PATH);
+	seprintf(tmp, lastof(tmp), "%s", SHARED_DIR);
+	AppendPathSeparator(tmp, lastof(tmp));
 	_searchpaths[SP_SHARED_DIR] = strdup(tmp);
 #else
 	_searchpaths[SP_SHARED_DIR] = NULL;
@@ -1141,7 +1140,7 @@ void DetermineBasePaths(const char *exe)
 	_searchpaths[SP_WORKING_DIR] = NULL;
 #else
 	if (getcwd(tmp, MAX_PATH) == NULL) *tmp = '\0';
-	AppendPathSeparator(tmp, MAX_PATH);
+	AppendPathSeparator(tmp, lastof(tmp));
 	_searchpaths[SP_WORKING_DIR] = strdup(tmp);
 #endif
 
@@ -1150,7 +1149,7 @@ void DetermineBasePaths(const char *exe)
 	/* Change the working directory to that one of the executable */
 	if (ChangeWorkingDirectoryToExecutable(exe)) {
 		if (getcwd(tmp, MAX_PATH) == NULL) *tmp = '\0';
-		AppendPathSeparator(tmp, MAX_PATH);
+		AppendPathSeparator(tmp, lastof(tmp));
 		_searchpaths[SP_BINARY_DIR] = strdup(tmp);
 	} else {
 		_searchpaths[SP_BINARY_DIR] = NULL;
@@ -1166,8 +1165,8 @@ void DetermineBasePaths(const char *exe)
 #if defined(__MORPHOS__) || defined(__AMIGA__) || defined(DOS) || defined(OS2)
 	_searchpaths[SP_INSTALLATION_DIR] = NULL;
 #else
-	snprintf(tmp, MAX_PATH, "%s", GLOBAL_DATA_DIR);
-	AppendPathSeparator(tmp, MAX_PATH);
+	seprintf(tmp, lastof(tmp), "%s", GLOBAL_DATA_DIR);
+	AppendPathSeparator(tmp, lastof(tmp));
 	_searchpaths[SP_INSTALLATION_DIR] = strdup(tmp);
 #endif
 #ifdef WITH_COCOA
@@ -1195,11 +1194,11 @@ void DeterminePaths(const char *exe)
 	char config_home[MAX_PATH];
 
 	const char *xdg_config_home = xdgConfigHome(NULL);
-	snprintf(config_home, MAX_PATH, "%s" PATHSEP "%s", xdg_config_home,
+	seprintf(config_home, lastof(config_home), "%s" PATHSEP "%s", xdg_config_home,
 			PERSONAL_DIR[0] == '.' ? &PERSONAL_DIR[1] : PERSONAL_DIR);
 	free(xdg_config_home);
 
-	AppendPathSeparator(config_home, MAX_PATH);
+	AppendPathSeparator(config_home, lastof(config_home));
 #endif
 
 	Searchpath sp;
@@ -1219,7 +1218,7 @@ void DeterminePaths(const char *exe)
 		}
 	} else {
 		char personal_dir[MAX_PATH];
-		if (FioFindFullPath(personal_dir, lengthof(personal_dir), BASE_DIR, "openttd.cfg") != NULL) {
+		if (FioFindFullPath(personal_dir, lastof(personal_dir), BASE_DIR, "openttd.cfg") != NULL) {
 			char *end = strrchr(personal_dir, PATHSEPCHAR);
 			if (end != NULL) end[1] = '\0';
 			config_dir = strdup(personal_dir);
@@ -1400,13 +1399,13 @@ static uint ScanPath(FileScanner *fs, const char *extension, const char *path, s
 
 		if (!FiosIsValidFile(path, dirent, &sb)) continue;
 
-		snprintf(filename, lengthof(filename), "%s%s", path, d_name);
+		seprintf(filename, lastof(filename), "%s%s", path, d_name);
 
 		if (S_ISDIR(sb.st_mode)) {
 			/* Directory */
 			if (!recursive) continue;
 			if (strcmp(d_name, ".") == 0 || strcmp(d_name, "..") == 0) continue;
-			if (!AppendPathSeparator(filename, lengthof(filename))) continue;
+			if (!AppendPathSeparator(filename, lastof(filename))) continue;
 			num += ScanPath(fs, extension, filename, basepath_length, recursive);
 		} else if (S_ISREG(sb.st_mode)) {
 			/* File */
@@ -1457,7 +1456,7 @@ uint FileScanner::Scan(const char *extension, Subdirectory sd, bool tars, bool r
 		/* Don't search in the working directory */
 		if (sp == SP_WORKING_DIR && !_do_scan_working_directory) continue;
 
-		FioAppendDirectory(path, MAX_PATH, sp, sd);
+		FioAppendDirectory(path, lastof(path), sp, sd);
 		num += ScanPath(this, extension, path, strlen(path), recursive);
 	}
 
@@ -1493,6 +1492,6 @@ uint FileScanner::Scan(const char *extension, const char *directory, bool recurs
 {
 	char path[MAX_PATH];
 	strecpy(path, directory, lastof(path));
-	if (!AppendPathSeparator(path, lengthof(path))) return 0;
+	if (!AppendPathSeparator(path, lastof(path))) return 0;
 	return ScanPath(this, extension, path, strlen(path), recursive);
 }
diff --git a/src/fileio_func.h b/src/fileio_func.h
index 449ba51fe5..443460b2d3 100644
--- a/src/fileio_func.h
+++ b/src/fileio_func.h
@@ -51,15 +51,15 @@ static inline bool IsValidSearchPath(Searchpath sp)
 void FioFCloseFile(FILE *f);
 FILE *FioFOpenFile(const char *filename, const char *mode, Subdirectory subdir, size_t *filesize = NULL);
 bool FioCheckFileExists(const char *filename, Subdirectory subdir);
-char *FioGetFullPath(char *buf, size_t buflen, Searchpath sp, Subdirectory subdir, const char *filename);
-char *FioFindFullPath(char *buf, size_t buflen, Subdirectory subdir, const char *filename);
-char *FioAppendDirectory(char *buf, size_t buflen, Searchpath sp, Subdirectory subdir);
-char *FioGetDirectory(char *buf, size_t buflen, Subdirectory subdir);
+char *FioGetFullPath(char *buf, const char *last, Searchpath sp, Subdirectory subdir, const char *filename);
+char *FioFindFullPath(char *buf, const char *last, Subdirectory subdir, const char *filename);
+char *FioAppendDirectory(char *buf, const char *last, Searchpath sp, Subdirectory subdir);
+char *FioGetDirectory(char *buf, const char *last, Subdirectory subdir);
 
 const char *FiosGetScreenshotDir();
 
 void SanitizeFilename(char *filename);
-bool AppendPathSeparator(char *buf, size_t buflen);
+bool AppendPathSeparator(char *buf, const char *last);
 void DeterminePaths(const char *exe);
 void *ReadFileToMem(const char *filename, size_t *lenp, size_t maxsize);
 bool FileExists(const char *filename);
diff --git a/src/fios.cpp b/src/fios.cpp
index ced425967a..43d781b5da 100644
--- a/src/fios.cpp
+++ b/src/fios.cpp
@@ -31,6 +31,7 @@
 /* Variables to display file lists */
 SmallVector<FiosItem, 32> _fios_items;
 static char *_fios_path;
+static const char *_fios_path_last;
 SmallFiosItem _file_to_saveload;
 SortingBits _savegame_sort_order = SORT_BY_DATE | SORT_DESCENDING;
 
@@ -91,14 +92,12 @@ StringID FiosGetDescText(const char **path, uint64 *total_free)
  */
 const char *FiosBrowseTo(const FiosItem *item)
 {
-	char *path = _fios_path;
-
 	switch (item->type) {
 		case FIOS_TYPE_DRIVE:
 #if defined(WINCE)
-			snprintf(path, MAX_PATH, PATHSEP "");
+			seprintf(_fios_path, _fios_path_last, PATHSEP "");
 #elif defined(WIN32) || defined(__OS2__)
-			snprintf(path, MAX_PATH, "%c:" PATHSEP, item->title[0]);
+			seprintf(_fios_path, _fios_path_last, "%c:" PATHSEP, item->title[0]);
 #endif
 			/* FALL THROUGH */
 		case FIOS_TYPE_INVALID:
@@ -106,16 +105,16 @@ const char *FiosBrowseTo(const FiosItem *item)
 
 		case FIOS_TYPE_PARENT: {
 			/* Check for possible NULL ptr (not required for UNIXes, but AmigaOS-alikes) */
-			char *s = strrchr(path, PATHSEPCHAR);
-			if (s != NULL && s != path) {
+			char *s = strrchr(_fios_path, PATHSEPCHAR);
+			if (s != NULL && s != _fios_path) {
 				s[0] = '\0'; // Remove last path separator character, so we can go up one level.
 			}
-			s = strrchr(path, PATHSEPCHAR);
+			s = strrchr(_fios_path, PATHSEPCHAR);
 			if (s != NULL) {
 				s[1] = '\0'; // go up a directory
 #if defined(__MORPHOS__) || defined(__AMIGAOS__)
 			/* On MorphOS or AmigaOS paths look like: "Volume:directory/subdirectory" */
-			} else if ((s = strrchr(path, ':')) != NULL) {
+			} else if ((s = strrchr(_fios_path, ':')) != NULL) {
 				s[1] = '\0';
 #endif
 			}
@@ -123,12 +122,12 @@ const char *FiosBrowseTo(const FiosItem *item)
 		}
 
 		case FIOS_TYPE_DIR:
-			strcat(path, item->name);
-			strcat(path, PATHSEP);
+			strecat(_fios_path, item->name, _fios_path_last);
+			strecat(_fios_path, PATHSEP, _fios_path_last);
 			break;
 
 		case FIOS_TYPE_DIRECT:
-			snprintf(path, MAX_PATH, "%s", item->name);
+			seprintf(_fios_path, _fios_path_last, "%s", item->name);
 			break;
 
 		case FIOS_TYPE_FILE:
@@ -149,9 +148,9 @@ const char *FiosBrowseTo(const FiosItem *item)
  * @param path Directory path, may be \c NULL.
  * @param name Filename.
  * @param ext Filename extension (use \c "" for no extension).
- * @param size Size of \a buf.
+ * @param last Last element of buffer \a buf.
  */
-static void FiosMakeFilename(char *buf, const char *path, const char *name, const char *ext, size_t size)
+static void FiosMakeFilename(char *buf, const char *path, const char *name, const char *ext, const char *last)
 {
 	const char *period;
 
@@ -163,15 +162,15 @@ static void FiosMakeFilename(char *buf, const char *path, const char *name, cons
 		unsigned char sepchar = path[(strlen(path) - 1)];
 
 		if (sepchar != ':' && sepchar != '/') {
-			snprintf(buf, size, "%s" PATHSEP "%s%s", path, name, ext);
+			seprintf(buf, last, "%s" PATHSEP "%s%s", path, name, ext);
 		} else {
-			snprintf(buf, size, "%s%s%s", path, name, ext);
+			seprintf(buf, last, "%s%s%s", path, name, ext);
 		}
 	} else {
-		snprintf(buf, size, "%s%s", name, ext);
+		seprintf(buf, last, "%s%s", name, ext);
 	}
 #else
-	snprintf(buf, size, "%s" PATHSEP "%s%s", path, name, ext);
+	seprintf(buf, last, "%s" PATHSEP "%s%s", path, name, ext);
 #endif
 }
 
@@ -179,28 +178,28 @@ static void FiosMakeFilename(char *buf, const char *path, const char *name, cons
  * Make a save game or scenario filename from a name.
  * @param buf Destination buffer for saving the filename.
  * @param name Name of the file.
- * @param size Length of buffer \a buf.
+ * @param last Last element of buffer \a buf.
  */
-void FiosMakeSavegameName(char *buf, const char *name, size_t size)
+void FiosMakeSavegameName(char *buf, const char *name, const char *last)
 {
 	const char *extension = (_game_mode == GM_EDITOR) ? ".scn" : ".sav";
 
-	FiosMakeFilename(buf, _fios_path, name, extension, size);
+	FiosMakeFilename(buf, _fios_path, name, extension, _fios_path_last);
 }
 
 /**
  * Construct a filename for a height map.
  * @param buf Destination buffer.
  * @param name Filename.
- * @param size Size of \a buf.
+ * @param last Last element of buffer \a buf.
  */
-void FiosMakeHeightmapName(char *buf, const char *name, size_t size)
+void FiosMakeHeightmapName(char *buf, const char *name, const char *last)
 {
 	char ext[5];
 	ext[0] = '.';
 	strecpy(ext + 1, GetCurrentScreenshotExtension(), lastof(ext));
 
-	FiosMakeFilename(buf, _fios_path, name, ext, size);
+	FiosMakeFilename(buf, _fios_path, name, ext, _fios_path_last);
 }
 
 /**
@@ -211,7 +210,7 @@ bool FiosDelete(const char *name)
 {
 	char filename[512];
 
-	FiosMakeSavegameName(filename, name, lengthof(filename));
+	FiosMakeSavegameName(filename, name, lastof(filename));
 	return unlink(filename) == 0;
 }
 
@@ -326,7 +325,7 @@ static void FiosGetFileList(SaveLoadDialogMode mode, fios_getlist_callback_proc
 				fios->type = FIOS_TYPE_DIR;
 				fios->mtime = 0;
 				strecpy(fios->name, d_name, lastof(fios->name));
-				snprintf(fios->title, lengthof(fios->title), "%s" PATHSEP " (Directory)", d_name);
+				seprintf(fios->title, lastof(fios->title), "%s" PATHSEP " (Directory)", d_name);
 				str_validate(fios->title, lastof(fios->title));
 			}
 		}
@@ -430,13 +429,16 @@ FiosType FiosGetSavegameListCallback(SaveLoadDialogMode mode, const char *file,
 void FiosGetSavegameList(SaveLoadDialogMode mode)
 {
 	static char *fios_save_path = NULL;
+	static char *fios_save_path_last = NULL;
 
 	if (fios_save_path == NULL) {
 		fios_save_path = MallocT<char>(MAX_PATH);
-		FioGetDirectory(fios_save_path, MAX_PATH, SAVE_DIR);
+		fios_save_path_last = fios_save_path + MAX_PATH - 1;
+		FioGetDirectory(fios_save_path, fios_save_path_last, SAVE_DIR);
 	}
 
 	_fios_path = fios_save_path;
+	_fios_path_last = fios_save_path_last;
 
 	FiosGetFileList(mode, &FiosGetSavegameListCallback, NO_DIRECTORY);
 }
@@ -481,17 +483,20 @@ static FiosType FiosGetScenarioListCallback(SaveLoadDialogMode mode, const char
 void FiosGetScenarioList(SaveLoadDialogMode mode)
 {
 	static char *fios_scn_path = NULL;
+	static char *fios_scn_path_last = NULL;
 
 	/* Copy the default path on first run or on 'New Game' */
 	if (fios_scn_path == NULL) {
 		fios_scn_path = MallocT<char>(MAX_PATH);
-		FioGetDirectory(fios_scn_path, MAX_PATH, SCENARIO_DIR);
+		fios_scn_path_last = fios_scn_path + MAX_PATH - 1;
+		FioGetDirectory(fios_scn_path, fios_scn_path_last, SCENARIO_DIR);
 	}
 
 	_fios_path = fios_scn_path;
+	_fios_path_last = fios_scn_path_last;
 
 	char base_path[MAX_PATH];
-	FioGetDirectory(base_path, sizeof(base_path), SCENARIO_DIR);
+	FioGetDirectory(base_path, lastof(base_path), SCENARIO_DIR);
 
 	FiosGetFileList(mode, &FiosGetScenarioListCallback, (mode == SLD_LOAD_SCENARIO && strcmp(base_path, _fios_path) == 0) ? SCENARIO_DIR : NO_DIRECTORY);
 }
@@ -524,7 +529,7 @@ static FiosType FiosGetHeightmapListCallback(SaveLoadDialogMode mode, const char
 		Searchpath sp;
 		FOR_ALL_SEARCHPATHS(sp) {
 			char buf[MAX_PATH];
-			FioAppendDirectory(buf, sizeof(buf), sp, HEIGHTMAP_DIR);
+			FioAppendDirectory(buf, lastof(buf), sp, HEIGHTMAP_DIR);
 
 			if (strncmp(buf, it->second.tar_filename, strlen(buf)) == 0) {
 				match = true;
@@ -547,16 +552,19 @@ static FiosType FiosGetHeightmapListCallback(SaveLoadDialogMode mode, const char
 void FiosGetHeightmapList(SaveLoadDialogMode mode)
 {
 	static char *fios_hmap_path = NULL;
+	static char *fios_hmap_path_last = NULL;
 
 	if (fios_hmap_path == NULL) {
 		fios_hmap_path = MallocT<char>(MAX_PATH);
-		FioGetDirectory(fios_hmap_path, MAX_PATH, HEIGHTMAP_DIR);
+		fios_hmap_path_last = fios_hmap_path + MAX_PATH - 1;
+		FioGetDirectory(fios_hmap_path, fios_hmap_path_last, HEIGHTMAP_DIR);
 	}
 
 	_fios_path = fios_hmap_path;
+	_fios_path_last = fios_hmap_path_last;
 
 	char base_path[MAX_PATH];
-	FioGetDirectory(base_path, sizeof(base_path), HEIGHTMAP_DIR);
+	FioGetDirectory(base_path, lastof(base_path), HEIGHTMAP_DIR);
 
 	FiosGetFileList(mode, &FiosGetHeightmapListCallback, strcmp(base_path, _fios_path) == 0 ? HEIGHTMAP_DIR : NO_DIRECTORY);
 }
@@ -571,7 +579,7 @@ const char *FiosGetScreenshotDir()
 
 	if (fios_screenshot_path == NULL) {
 		fios_screenshot_path = MallocT<char>(MAX_PATH);
-		FioGetDirectory(fios_screenshot_path, MAX_PATH, SCREENSHOT_DIR);
+		FioGetDirectory(fios_screenshot_path, fios_screenshot_path + MAX_PATH - 1, SCREENSHOT_DIR);
 	}
 
 	return fios_screenshot_path;
diff --git a/src/fios.h b/src/fios.h
index 43a018f260..b26fe00925 100644
--- a/src/fios.h
+++ b/src/fios.h
@@ -170,8 +170,8 @@ const char *FiosBrowseTo(const FiosItem *item);
 
 StringID FiosGetDescText(const char **path, uint64 *total_free);
 bool FiosDelete(const char *name);
-void FiosMakeHeightmapName(char *buf, const char *name, size_t size);
-void FiosMakeSavegameName(char *buf, const char *name, size_t size);
+void FiosMakeHeightmapName(char *buf, const char *name, const char *last);
+void FiosMakeSavegameName(char *buf, const char *name, const char *last);
 
 FiosType FiosGetSavegameListCallback(SaveLoadDialogMode mode, const char *file, const char *ext, char *title, const char *last);
 
diff --git a/src/fios_gui.cpp b/src/fios_gui.cpp
index 579eedf894..5c91ec77d7 100644
--- a/src/fios_gui.cpp
+++ b/src/fios_gui.cpp
@@ -298,17 +298,17 @@ public:
 		switch (_saveload_mode) {
 			case SLD_SAVE_GAME:
 			case SLD_LOAD_GAME:
-				FioGetDirectory(o_dir.name, lengthof(o_dir.name), SAVE_DIR);
+				FioGetDirectory(o_dir.name, lastof(o_dir.name), SAVE_DIR);
 				break;
 
 			case SLD_SAVE_SCENARIO:
 			case SLD_LOAD_SCENARIO:
-				FioGetDirectory(o_dir.name, lengthof(o_dir.name), SCENARIO_DIR);
+				FioGetDirectory(o_dir.name, lastof(o_dir.name), SCENARIO_DIR);
 				break;
 
 			case SLD_SAVE_HEIGHTMAP:
 			case SLD_LOAD_HEIGHTMAP:
-				FioGetDirectory(o_dir.name, lengthof(o_dir.name), HEIGHTMAP_DIR);
+				FioGetDirectory(o_dir.name, lastof(o_dir.name), HEIGHTMAP_DIR);
 				break;
 
 			default:
@@ -654,10 +654,10 @@ public:
 		} else if (this->IsWidgetLowered(WID_SL_SAVE_GAME)) { // Save button clicked
 			if (_saveload_mode  == SLD_SAVE_GAME || _saveload_mode == SLD_SAVE_SCENARIO) {
 				_switch_mode = SM_SAVE_GAME;
-				FiosMakeSavegameName(_file_to_saveload.name, this->filename_editbox.text.buf, sizeof(_file_to_saveload.name));
+				FiosMakeSavegameName(_file_to_saveload.name, this->filename_editbox.text.buf, lastof(_file_to_saveload.name));
 			} else {
 				_switch_mode = SM_SAVE_HEIGHTMAP;
-				FiosMakeHeightmapName(_file_to_saveload.name, this->filename_editbox.text.buf, sizeof(_file_to_saveload.name));
+				FiosMakeHeightmapName(_file_to_saveload.name, this->filename_editbox.text.buf, lastof(_file_to_saveload.name));
 			}
 
 			/* In the editor set up the vehicle engines correctly (date might have changed) */
diff --git a/src/music_gui.cpp b/src/music_gui.cpp
index 01406849fe..c9eb21aa37 100644
--- a/src/music_gui.cpp
+++ b/src/music_gui.cpp
@@ -182,8 +182,8 @@ static void MusicVolumeChanged(byte new_vol)
 static void DoPlaySong()
 {
 	char filename[MAX_PATH];
-	if (FioFindFullPath(filename, lengthof(filename), BASESET_DIR, BaseMusic::GetUsedSet()->files[_music_wnd_cursong - 1].filename) == NULL) {
-		FioFindFullPath(filename, lengthof(filename), OLD_GM_DIR, BaseMusic::GetUsedSet()->files[_music_wnd_cursong - 1].filename);
+	if (FioFindFullPath(filename, lastof(filename), BASESET_DIR, BaseMusic::GetUsedSet()->files[_music_wnd_cursong - 1].filename) == NULL) {
+		FioFindFullPath(filename, lastof(filename), OLD_GM_DIR, BaseMusic::GetUsedSet()->files[_music_wnd_cursong - 1].filename);
 	}
 	_music_driver->PlaySong(filename);
 	SetWindowDirty(WC_MUSIC_WINDOW, 0);
diff --git a/src/network/network_content.cpp b/src/network/network_content.cpp
index 215ed5dfdd..174dbdafe6 100644
--- a/src/network/network_content.cpp
+++ b/src/network/network_content.cpp
@@ -390,7 +390,7 @@ static char *GetFullFilename(const ContentInfo *ci, bool compressed)
 	if (dir == NO_DIRECTORY) return NULL;
 
 	static char buf[MAX_PATH];
-	FioGetFullPath(buf, lengthof(buf), SP_AUTODOWNLOAD_DIR, dir, ci->filename);
+	FioGetFullPath(buf, lastof(buf), SP_AUTODOWNLOAD_DIR, dir, ci->filename);
 	strecat(buf, compressed ? ".tar.gz" : ".tar", lastof(buf));
 
 	return buf;
diff --git a/src/script/script_instance.cpp b/src/script/script_instance.cpp
index eab85d74b6..9cfe05c490 100644
--- a/src/script/script_instance.cpp
+++ b/src/script/script_instance.cpp
@@ -116,7 +116,7 @@ bool ScriptInstance::LoadCompatibilityScripts(const char *api_version, Subdirect
 	char buf[MAX_PATH];
 	Searchpath sp;
 	FOR_ALL_SEARCHPATHS(sp) {
-		FioAppendDirectory(buf, MAX_PATH, sp, dir);
+		FioAppendDirectory(buf, lastof(buf), sp, dir);
 		strecat(buf, script_name, lastof(buf));
 		if (!FileExists(buf)) continue;
 
diff --git a/src/strings.cpp b/src/strings.cpp
index 23a8804ab7..1b95f4251a 100644
--- a/src/strings.cpp
+++ b/src/strings.cpp
@@ -1954,7 +1954,7 @@ void InitializeLanguagePacks()
 
 	FOR_ALL_SEARCHPATHS(sp) {
 		char path[MAX_PATH];
-		FioAppendDirectory(path, lengthof(path), sp, LANG_DIR);
+		FioAppendDirectory(path, lastof(path), sp, LANG_DIR);
 		GetLanguageList(path);
 	}
 	if (_languages.Length() == 0) usererror("No available language packs (invalid versions?)");
diff --git a/src/video/sdl_v.cpp b/src/video/sdl_v.cpp
index 6ec5269d5d..9b1dd727f8 100644
--- a/src/video/sdl_v.cpp
+++ b/src/video/sdl_v.cpp
@@ -282,7 +282,7 @@ bool VideoDriver_SDL::CreateMainSurface(uint w, uint h)
 	if (bpp == 0) usererror("Can't use a blitter that blits 0 bpp for normal visuals");
 
 	char icon_path[MAX_PATH];
-	if (FioFindFullPath(icon_path, lengthof(icon_path), BASESET_DIR, "openttd.32.bmp") != NULL) {
+	if (FioFindFullPath(icon_path, lastof(icon_path), BASESET_DIR, "openttd.32.bmp") != NULL) {
 		/* Give the application an icon */
 		icon = SDL_CALL SDL_LoadBMP(icon_path);
 		if (icon != NULL) {