diff --git a/source/c01/p10_remove_duplicates_from_seq_order.rst b/source/c01/p10_remove_duplicates_from_seq_order.rst
index 168da124..b67d560e 100644
--- a/source/c01/p10_remove_duplicates_from_seq_order.rst
+++ b/source/c01/p10_remove_duplicates_from_seq_order.rst
@@ -19,7 +19,7 @@
         for item in items:
             if item not in seen:
                 yield item
-                seen.add(item)
+            seen.add(item)
 下面是使用上述函数的例子：
 
 .. code-block:: python