diff --git a/prototype/Doubt/Cofree.swift b/prototype/Doubt/Cofree.swift
index 2bd234be5..7e3378463 100644
--- a/prototype/Doubt/Cofree.swift
+++ b/prototype/Doubt/Cofree.swift
@@ -1,5 +1,5 @@
 //  Copyright © 2015 GitHub. All rights reserved.
 
-public enum Cofree {
-
+public enum Cofree<B> {
+	case Unroll(B)
 }