diff --git a/prototype/Doubt/Algorithm.swift b/prototype/Doubt/Algorithm.swift
index 1b2181cbe..b2295e0ab 100644
--- a/prototype/Doubt/Algorithm.swift
+++ b/prototype/Doubt/Algorithm.swift
@@ -76,8 +76,8 @@ public enum Algorithm<Term: TermType, B> {
 
 		case let .Roll(.ByKey(a, b, f)):
 			// Essentially [set reconciliation](https://en.wikipedia.org/wiki/Data_synchronization#Unordered_data) on the keys, followed by recurring into the values of the intersecting keys.
-			let deleted = Set(a.keys).subtract(b.keys).map { ($0, Diff.Pure(Patch.Delete(a[$0]!))) }
-			let inserted = Set(b.keys).subtract(a.keys).map { ($0, Diff.Pure(Patch.Insert(b[$0]!))) }
+			let deleted = Set(a.keys).subtract(b.keys).map { ($0, Diff.Delete(a[$0]!)) }
+			let inserted = Set(b.keys).subtract(a.keys).map { ($0, Diff.Insert(b[$0]!)) }
 			let patched = Set(a.keys).intersect(b.keys).map { ($0, recurOrReplace(a[$0]!, b[$0]!)) }
 			return f(Dictionary(elements: deleted + inserted + patched)).evaluate(equals, recur: recur)