diff --git a/authfs/src/file.rs b/authfs/src/file.rs
index 9ff8ea5..4b43786 100644
--- a/authfs/src/file.rs
+++ b/authfs/src/file.rs
@@ -49,4 +49,7 @@
         }
         Ok(())
     }
+
+    /// Resizes the file to the new size.
+    fn resize(&self, size: u64) -> io::Result<()>;
 }