diff --git a/templatestrings.go b/templatestrings.go
index 83ef8a1..54c3913 100644
--- a/templatestrings.go
+++ b/templatestrings.go
@@ -26,7 +26,7 @@ func InitTemplateStringsFS(filesystem fs.FS, stringsDir string, fileExt string,
 		defaultVariant,
 	}
 	// Check directory
-	if stat, err := os.Stat(stringsDir); err != nil {
+	if stat, err := fs.Stat(filesystem, stringsDir); err != nil {
 		return nil, err
 	} else if !stat.IsDir() {
 		return nil, errors.New("specified directory is no dir")
@@ -42,7 +42,7 @@ func InitTemplateStringsFS(filesystem fs.FS, stringsDir string, fileExt string,
 		if _, ok := ts.templateStrings[variant]; ok {
 			continue
 		}
-		fb, err := os.ReadFile(filepath.Join(stringsDir, variant+fileExt))
+		fb, err := fs.ReadFile(filesystem, filepath.Join(stringsDir, variant+fileExt))
 		if err != nil {
 			// Just ignore the file
 			continue