diff --git a/Control/Applicative/Backwards.hs b/Control/Applicative/Backwards.hs
--- a/Control/Applicative/Backwards.hs
+++ b/Control/Applicative/Backwards.hs
@@ -27,6 +27,9 @@
     Backwards(..),
   ) where
 
+#if MIN_VERSION_base(4,18,0)
+import Data.Foldable1 (Foldable1(foldMap1))
+#endif
 import Data.Functor.Classes
 #if MIN_VERSION_base(4,12,0)
 import Data.Functor.Contravariant
@@ -120,7 +123,14 @@
     length (Backwards t) = length t
 #endif
 
+#if MIN_VERSION_base(4,18,0)
 -- | Derived instance.
+instance (Foldable1 f) => Foldable1 (Backwards f) where
+    foldMap1 f (Backwards t) = foldMap1 f t
+    {-# INLINE foldMap1 #-}
+#endif
+
+-- | Derived instance.
 instance (Traversable f) => Traversable (Backwards f) where
     traverse f (Backwards t) = fmap Backwards (traverse f t)
     {-# INLINE traverse #-}
@@ -129,7 +139,7 @@
 
 #if MIN_VERSION_base(4,12,0)
 -- | Derived instance.
-instance Contravariant f => Contravariant (Backwards f) where
+instance (Contravariant f) => Contravariant (Backwards f) where
     contramap f = Backwards . contramap f . forwards
     {-# INLINE contramap #-}
 #endif
diff --git a/Control/Applicative/Lift.hs b/Control/Applicative/Lift.hs
--- a/Control/Applicative/Lift.hs
+++ b/Control/Applicative/Lift.hs
@@ -32,6 +32,9 @@
     eitherToErrors
   ) where
 
+#if MIN_VERSION_base(4,18,0)
+import Data.Foldable1 (Foldable1(foldMap1))
+#endif
 import Data.Functor.Classes
 
 import Control.Applicative
@@ -114,6 +117,13 @@
     Other _ <|> Pure y = Pure y
     Other x <|> Other y = Other (x <|> y)
     {-# INLINE (<|>) #-}
+
+#if MIN_VERSION_base(4,18,0)
+instance (Foldable1 f) => Foldable1 (Lift f) where
+    foldMap1 f (Pure x)  = f x
+    foldMap1 f (Other y) = foldMap1 f y
+    {-# INLINE foldMap1 #-}
+#endif
 
 -- | Projection to the other functor.
 unLift :: (Applicative f) => Lift f a -> f a
diff --git a/Control/Monad/Trans/Identity.hs b/Control/Monad/Trans/Identity.hs
--- a/Control/Monad/Trans/Identity.hs
+++ b/Control/Monad/Trans/Identity.hs
@@ -36,6 +36,9 @@
 import Control.Monad.IO.Class (MonadIO(liftIO))
 import Control.Monad.Signatures
 import Control.Monad.Trans.Class (MonadTrans(lift))
+#if MIN_VERSION_base(4,18,0)
+import Data.Foldable1 (Foldable1(foldMap1))
+#endif
 import Data.Functor.Classes
 #if MIN_VERSION_base(4,12,0)
 import Data.Functor.Contravariant
@@ -108,6 +111,12 @@
     length (IdentityT t) = length t
 #endif
 
+#if MIN_VERSION_base(4,18,0)
+instance (Foldable1 m) => Foldable1 (IdentityT m) where
+    foldMap1 f (IdentityT t) = foldMap1 f t
+    {-# INLINE foldMap1 #-}
+#endif
+
 instance (Traversable f) => Traversable (IdentityT f) where
     traverse f (IdentityT a) = IdentityT <$> traverse f a
     {-# INLINE traverse #-}
@@ -171,7 +180,7 @@
     {-# INLINE lift #-}
 
 #if MIN_VERSION_base(4,12,0)
-instance Contravariant f => Contravariant (IdentityT f) where
+instance (Contravariant f) => Contravariant (IdentityT f) where
     contramap f = IdentityT . contramap f . runIdentityT
     {-# INLINE contramap #-}
 #endif
diff --git a/Control/Monad/Trans/State/Lazy.hs b/Control/Monad/Trans/State/Lazy.hs
--- a/Control/Monad/Trans/State/Lazy.hs
+++ b/Control/Monad/Trans/State/Lazy.hs
@@ -56,6 +56,7 @@
     put,
     modify,
     modify',
+    modifyM,
     gets,
     -- * Lifting other operations
     liftCallCC,
@@ -299,6 +300,14 @@
     s <- get
     put $! f s
 {-# INLINE modify' #-}
+
+-- | A variant of 'modify' in which the new state is generated by a
+-- monadic action.
+modifyM :: (Monad m) => (s -> m s) -> StateT s m ()
+modifyM f = StateT $ \ s -> do
+    s' <- f s
+    return ((), s')
+{-# INLINE modifyM #-}
 
 -- | Get a specific component of the state, using a projection function
 -- supplied.
diff --git a/Control/Monad/Trans/State/Strict.hs b/Control/Monad/Trans/State/Strict.hs
--- a/Control/Monad/Trans/State/Strict.hs
+++ b/Control/Monad/Trans/State/Strict.hs
@@ -53,6 +53,7 @@
     put,
     modify,
     modify',
+    modifyM,
     gets,
     -- * Lifting other operations
     liftCallCC,
@@ -300,6 +301,14 @@
     s <- get
     put $! f s
 {-# INLINE modify' #-}
+
+-- | A variant of 'modify' in which the new state is generated by a
+-- monadic action.
+modifyM :: (Monad m) => (s -> m s) -> StateT s m ()
+modifyM f = StateT $ \ s -> do
+    s' <- f s
+    return ((), s')
+{-# INLINE modifyM #-}
 
 -- | Get a specific component of the state, using a projection function
 -- supplied.
diff --git a/Data/Functor/Reverse.hs b/Data/Functor/Reverse.hs
--- a/Data/Functor/Reverse.hs
+++ b/Data/Functor/Reverse.hs
@@ -28,6 +28,9 @@
   ) where
 
 import Control.Applicative.Backwards
+#if MIN_VERSION_base(4,18,0)
+import Data.Foldable1 (Foldable1(foldMap1))
+#endif
 import Data.Functor.Classes
 #if MIN_VERSION_base(4,12,0)
 import Data.Functor.Contravariant
@@ -140,6 +143,12 @@
     length (Reverse t) = length t
 #endif
 
+#if MIN_VERSION_base(4,18,0)
+-- | Fold from right to left.
+instance (Foldable1 f) => Foldable1 (Reverse f) where
+    foldMap1 f (Reverse t) = getDual (foldMap1 (Dual . f) t)
+#endif
+
 -- | Traverse from right to left.
 instance (Traversable f) => Traversable (Reverse f) where
     traverse f (Reverse t) =
@@ -148,7 +157,7 @@
 
 #if MIN_VERSION_base(4,12,0)
 -- | Derived instance.
-instance Contravariant f => Contravariant (Reverse f) where
+instance (Contravariant f) => Contravariant (Reverse f) where
     contramap f = Reverse . contramap f . getReverse
     {-# INLINE contramap #-}
 #endif
diff --git a/changelog b/changelog
--- a/changelog
+++ b/changelog
@@ -1,5 +1,9 @@
 -*-change-log-*-
 
+0.6.1.0 Ross Paterson <R.Paterson@city.ac.uk> Feb 2023
+	* Add instances of Foldable1 (class added to base-4.18)
+	* Add modifyM to StateT transformers
+
 0.6.0.6 Ross Paterson <R.Paterson@city.ac.uk> Jan 2023
 	* Fix for GHC 8.6
 
diff --git a/transformers.cabal b/transformers.cabal
--- a/transformers.cabal
+++ b/transformers.cabal
@@ -1,5 +1,5 @@
 name:         transformers
-version:      0.6.0.6
+version:      0.6.1.0
 license:      BSD3
 license-file: LICENSE
 author:       Andy Gill, Ross Paterson