diff --git a/src/drivers/vfs.rs b/src/drivers/vfs.rs
index 0051c44e..56aa5f54 100644
--- a/src/drivers/vfs.rs
+++ b/src/drivers/vfs.rs
@@ -37,3 +37,9 @@ impl AbstractFilesystem for Vfs {
         Ok(self.0.get(&*rel_path).map(Clone::clone).unwrap_or_default())
     }
 }
+
+impl AbstractFilesystem for &Vfs {
+    fn file_names_in(&self, rel_path: &str) -> io::Result<HashSet<Box<str>>> {
+        (*self).file_names_in(rel_path)
+    }
+}