diff --git a/docs/advanced/serial.rst b/docs/advanced/serial.rst
index 05d5f37c7..8c0f83746 100644
--- a/docs/advanced/serial.rst
+++ b/docs/advanced/serial.rst
@@ -13,7 +13,7 @@ Serializable Class
 ========================
 
 ``Qlib`` provides a base class ``qlib.utils.serial.Serializable``, whose state can be dumped into or loaded from disk in `pickle` format. 
-When users dump the state of the ``Serializable`` instance, the attributes of the instance whose name **does not** start with `_` will be saved on the disk.
+When users dump the state of a ``Serializable`` instance, the attributes of the instance whose name **does not** start with `_` will be saved on the disk.
 
 Example
 ==========================