diff --git a/quickspec.cabal b/quickspec.cabal
--- a/quickspec.cabal
+++ b/quickspec.cabal
@@ -1,5 +1,5 @@
 Name:                quickspec
-Version:             2.2.1
+Version:             2.2.2
 Cabal-version:       >= 1.10
 Build-type:          Simple
 
@@ -109,10 +109,10 @@
     containers,
     data-lens-light >= 0.1.1,
     dlist,
-    hashable >= 1.5,
+    hashable >= 1.3,
     random,
     spoon,
     template-haskell,
     transformers,
-    twee-lib >= 2.6,
+    twee-lib == 2.7.1,
     uglymemo
diff --git a/src/QuickSpec/Internal/Pruning/UntypedTwee.hs b/src/QuickSpec/Internal/Pruning/UntypedTwee.hs
--- a/src/QuickSpec/Internal/Pruning/UntypedTwee.hs
+++ b/src/QuickSpec/Internal/Pruning/UntypedTwee.hs
@@ -177,7 +177,7 @@
   completePure config $
     addAxiom config state axiom
   where
-    axiom = Axiom 0 (prettyShow (t :=: u)) (toTwee t Twee.:=: toTwee u)
+    axiom = Axiom 0 (prettyShow (t :=: u)) Nothing (toTwee t Twee.:=: toTwee u)
 
 toTwee :: (Ord f, Twee.Intern f) =>
   Term f -> Twee.Term (Extended f)