diff --git a/pkg/proto/lib/UntypedLambda.hs b/pkg/proto/lib/UntypedLambda.hs
index 8a119ed092..4891756f35 100644
--- a/pkg/proto/lib/UntypedLambda.hs
+++ b/pkg/proto/lib/UntypedLambda.hs
@@ -3,7 +3,7 @@ module UntypedLambda where
 import ClassyPrelude
 
 import Bound
-import Control.Monad.Writer
+import Control.Monad.Writer hiding (fix)
 import Data.Deriving (deriveEq1, deriveOrd1, deriveRead1, deriveShow1)
 import qualified Data.Function as F
 import Data.List (elemIndex)
@@ -307,6 +307,10 @@ posIn i n
 copy :: Ord a => Exp a -> Nock
 copy = copyToNock . toCopy
 
+-- | Decrements its argument.
+decrement :: Exp String
+decrement = lam "a" $ App (fix "f" $ lam "b" $ Ift (Eql (Var "a") (Suc (Var "b"))) (Var "b") (App (Var "f") (Suc (Var "b")))) (Atm 0)
+
 -- x. y. x
 -- old: [8 [1 0] [1 8 [1 0] [1 0 30] 0 1] 0 1]
 --      =+  0  =