diff --git a/source/chapter2/22_Protocols.md b/source/chapter2/22_Protocols.md
index 2c119533..519c24ca 100644
--- a/source/chapter2/22_Protocols.md
+++ b/source/chapter2/22_Protocols.md
@@ -208,17 +208,17 @@ protocol Togglable {
 
 ```swift
 enum OnOffSwitch: Togglable {
-	case Off, On
-	mutating func toggle() {
-		switch self {
-		case Off:
-			self = On
-		case On:
-			self = Off
-		}
-	}
+    case off, on
+    mutating func toggle() {
+        switch self {
+        case .off:
+            self = .on
+        case .on:
+            self = .off
+        }
+    }
 }
-var lightSwitch = OnOffSwitch.Off
+var lightSwitch = OnOffSwitch.off
 lightSwitch.toggle()
 // lightSwitch 现在的值为 .On
 ```