diff --git a/deferred-folds.cabal b/deferred-folds.cabal
--- a/deferred-folds.cabal
+++ b/deferred-folds.cabal
@@ -1,7 +1,7 @@
 name:
   deferred-folds
 version:
-  0.6.5.1
+  0.6.6
 category:
   Folding
 synopsis:
@@ -46,4 +46,5 @@
   build-depends:
     base >=4.7 && <5,
     containers >=0.5 && <0.6,
-    foldl >=1 && <2
+    foldl >=1 && <2,
+    transformers >=0.5 && <0.6
diff --git a/library/DeferredFolds/Prelude.hs b/library/DeferredFolds/Prelude.hs
--- a/library/DeferredFolds/Prelude.hs
+++ b/library/DeferredFolds/Prelude.hs
@@ -82,3 +82,7 @@
 -- foldl
 -------------------------
 import Control.Foldl as Exports (Fold(..), FoldM(..))
+
+-- transformers
+-------------------------
+import Control.Monad.Trans.Class as Exports
diff --git a/library/DeferredFolds/UnfoldM.hs b/library/DeferredFolds/UnfoldM.hs
--- a/library/DeferredFolds/UnfoldM.hs
+++ b/library/DeferredFolds/UnfoldM.hs
@@ -41,6 +41,9 @@
   mzero = empty
   mplus = (<|>)
 
+instance MonadTrans UnfoldM where
+  lift m = UnfoldM (\ step init -> m >>= step init)
+
 instance Monad m => Semigroup (UnfoldM m a) where
   (<>) = (<|>)