diff --git a/en/src/method.md b/en/src/method.md
index 477ddcc..d103e26 100644
--- a/en/src/method.md
+++ b/en/src/method.md
@@ -174,7 +174,7 @@ impl TrafficLight {
     }
 
     // fill in the blank, DON'T use any variants of `Self`
-    pub fn change_state() {
+    pub fn change_state(__) {
         self.color = "green".to_string()
     }
 }
diff --git a/zh-CN/src/method.md b/zh-CN/src/method.md
index 5d20ee9..87f44ac 100644
--- a/zh-CN/src/method.md
+++ b/zh-CN/src/method.md
@@ -168,7 +168,7 @@ impl TrafficLight {
     }
 
     // 填空，不要使用 `Self` 或其变体
-    pub fn change_state() {
+    pub fn change_state(__) {
         self.color = "green".to_string()
     }
 }