diff --git a/source/chapter2/21_Protocols.md b/source/chapter2/21_Protocols.md
index 98143593..8efa003a 100755
--- a/source/chapter2/21_Protocols.md
+++ b/source/chapter2/21_Protocols.md
@@ -411,7 +411,7 @@ println(d12.asText())
 `SnakesAndLadders`类也可以通过`扩展`的方式来遵循协议：
 
 ```swift
-extension SnakeAndLadders: TextRepresentable {
+extension SnakesAndLadders: TextRepresentable {
 	func asText() -> String {
 		return "A game of Snakes and Ladders with \(finalSquare) squares"
 	}