diff --git a/prototype/Doubt/Interpreter.swift b/prototype/Doubt/Interpreter.swift
index 57ebe90e0..e0b323ffa 100644
--- a/prototype/Doubt/Interpreter.swift
+++ b/prototype/Doubt/Interpreter.swift
@@ -45,7 +45,7 @@ public struct Interpreter<Term: CofreeType> {
 		// If both terms are equal, we don’t need to bother diffing.
 		//
 		// In that case, zip the two terms together (to pair their annotations), and then map the resulting `Term` (which, since the terms are equal, will be non-nil) into a `Diff`.
-		if equal(a, b) { return hylo(Diff.Roll, Cofree.eliminate)(Term.zip(a, b)!) }
+		if equal(a, b) { return Diff(Term.zip(a, b)!) }
 		guard comparable(a, b) else { return nil }
 
 		let algorithm: Algorithm<Term, Diff>