diff --git a/Source/ResponseSerialization.swift b/Source/ResponseSerialization.swift
index 7b7d2b3ccd0aa5889bf81c5d59e010c3be272c4b..d47e69669667ae57ea34e2b77af7feb5a215dedf 100644
--- a/Source/ResponseSerialization.swift
+++ b/Source/ResponseSerialization.swift
@@ -30,6 +30,8 @@ import Foundation
 public protocol ResponseSerializer {
     /// The type of serialized object to be created by this `ResponseSerializer`.
     typealias SerializedObject
+
+    /// The type of error to be created by this `ResponseSerializer` if serialization fails.
     typealias Error: ErrorType
 
     /**