diff --git a/src/fileio.cpp b/src/fileio.cpp
index 92707b58e4..13b0e26f5b 100644
--- a/src/fileio.cpp
+++ b/src/fileio.cpp
@@ -68,7 +68,7 @@ TarFileList _tar_filelist[NUM_SUBDIRS];
 typedef std::map<std::string, std::string> TarLinkList;
 static TarLinkList _tar_linklist[NUM_SUBDIRS]; ///< List of directory links
 
-extern bool FiosIsValidFile(const char *path, const struct dirent *ent, struct stat *sb);
+extern bool FiosIsValidFile(const std::string &path, const struct dirent *ent, struct stat *sb);
 
 /**
  * Checks whether the given search path is a valid search path
diff --git a/src/fios.cpp b/src/fios.cpp
index f5444fdb0b..2f33f40cfc 100644
--- a/src/fios.cpp
+++ b/src/fios.cpp
@@ -36,7 +36,7 @@ SortingBits _savegame_sort_order = SORT_BY_DATE | SORT_DESCENDING;
 
 /* OS-specific functions are taken from their respective files (win32/unix/os2 .c) */
 extern bool FiosIsRoot(const char *path);
-extern bool FiosIsValidFile(const char *path, const struct dirent *ent, struct stat *sb);
+extern bool FiosIsValidFile(const std::string &path, const struct dirent *ent, struct stat *sb);
 extern bool FiosIsHiddenFile(const struct dirent *ent);
 extern void FiosGetDrives(FileList &file_list);
 extern bool FiosGetDiskFreeSpace(const char *path, uint64 *tot);
@@ -381,7 +381,7 @@ static void FiosGetFileList(SaveLoadOperation fop, fios_getlist_callback_proc *c
 			std::string d_name = FS2OTTD(dirent->d_name);
 
 			/* found file must be directory, but not '.' or '..' */
-			if (FiosIsValidFile(_fios_path->c_str(), dirent, &sb) && S_ISDIR(sb.st_mode) &&
+			if (FiosIsValidFile(*_fios_path, dirent, &sb) && S_ISDIR(sb.st_mode) &&
 					(!FiosIsHiddenFile(dirent) || StrStartsWithIgnoreCase(PERSONAL_DIR, d_name)) &&
 					d_name != "." && d_name != "..") {
 				fios = &file_list.emplace_back();
diff --git a/src/os/os2/os2.cpp b/src/os/os2/os2.cpp
index 235478ff27..e3913d7289 100644
--- a/src/os/os2/os2.cpp
+++ b/src/os/os2/os2.cpp
@@ -120,12 +120,10 @@ bool FiosGetDiskFreeSpace(const char *path, uint64 *tot)
 #endif
 }
 
-bool FiosIsValidFile(const char *path, const struct dirent *ent, struct stat *sb)
+bool FiosIsValidFile(const std::string &path, const struct dirent *ent, struct stat *sb)
 {
-	char filename[MAX_PATH];
-
-	snprintf(filename, lengthof(filename), "%s" PATHSEP "%s", path, ent->d_name);
-	return stat(filename, sb) == 0;
+	std::string filename = fmt::format("{}" PATHSEP "{}", path, ent->d_name);
+	return stat(filename.c_str(), sb) == 0;
 }
 
 bool FiosIsHiddenFile(const struct dirent *ent)
diff --git a/src/os/unix/unix.cpp b/src/os/unix/unix.cpp
index 8fa259454b..0f18a977e1 100644
--- a/src/os/unix/unix.cpp
+++ b/src/os/unix/unix.cpp
@@ -86,18 +86,13 @@ bool FiosGetDiskFreeSpace(const char *path, uint64 *tot)
 	return true;
 }
 
-bool FiosIsValidFile(const char *path, const struct dirent *ent, struct stat *sb)
+bool FiosIsValidFile(const std::string &path, const struct dirent *ent, struct stat *sb)
 {
-	char filename[MAX_PATH];
-	int res;
-	assert(path[strlen(path) - 1] == PATHSEPCHAR);
-	if (strlen(path) > 2) assert(path[strlen(path) - 2] != PATHSEPCHAR);
-	res = seprintf(filename, lastof(filename), "%s%s", path, ent->d_name);
+	assert(path.back() == PATHSEPCHAR);
+	if (path.size() > 2) assert(path[path.size() - 2] != PATHSEPCHAR);
+	std::string filename = fmt::format("{}{}", path, ent->d_name);
 
-	/* Could we fully concatenate the path and filename? */
-	if (res >= (int)lengthof(filename) || res < 0) return false;
-
-	return stat(filename, sb) == 0;
+	return stat(filename.c_str(), sb) == 0;
 }
 
 bool FiosIsHiddenFile(const struct dirent *ent)
diff --git a/src/os/windows/win32.cpp b/src/os/windows/win32.cpp
index affa3c9dc9..54bf06249f 100644
--- a/src/os/windows/win32.cpp
+++ b/src/os/windows/win32.cpp
@@ -190,7 +190,7 @@ void FiosGetDrives(FileList &file_list)
 	}
 }
 
-bool FiosIsValidFile(const char *path, const struct dirent *ent, struct stat *sb)
+bool FiosIsValidFile(const std::string &path, const struct dirent *ent, struct stat *sb)
 {
 	/* hectonanoseconds between Windows and POSIX epoch */
 	static const int64 posix_epoch_hns = 0x019DB1DED53E8000LL;