diff --git a/effectful/src/Effectful/Concurrent/MVar.hs b/effectful/src/Effectful/Concurrent/MVar.hs
index 719dbe6..edc21b6 100644
--- a/effectful/src/Effectful/Concurrent/MVar.hs
+++ b/effectful/src/Effectful/Concurrent/MVar.hs
@@ -81,31 +81,37 @@ tryReadMVar = unsafeEff_ . M.tryReadMVar
 withMVar :: Concurrent :> es => MVar a -> (a -> Eff es b) -> Eff es b
 withMVar var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.withMVar var $ unlift . f
+{-# INLINE withMVar #-}
 
 -- | Lifted 'M.withMVarMasked'.
 withMVarMasked :: Concurrent :> es => MVar a -> (a -> Eff es b) -> Eff es b
 withMVarMasked var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.withMVarMasked var $ unlift . f
+{-# INLINE withMVarMasked #-}
 
 -- | Lifted 'M.modifyMVar_'.
 modifyMVar_ :: Concurrent :> es => MVar a -> (a -> Eff es a) -> Eff es ()
 modifyMVar_ var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.modifyMVar_ var $ unlift . f
+{-# INLINE modifyMVar_ #-}
 
 -- | Lifted 'M.modifyMVar'.
 modifyMVar :: Concurrent :> es => MVar a -> (a -> Eff es (a, b)) -> Eff es b
 modifyMVar var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.modifyMVar var $ unlift . f
+{-# INLINE modifyMVar #-}
 
 -- | Lifted 'M.modifyMVarMasked_'.
 modifyMVarMasked_ :: Concurrent :> es => MVar a -> (a -> Eff es a) -> Eff es ()
 modifyMVarMasked_ var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.modifyMVarMasked_ var $ unlift . f
+{-# INLINE modifyMVarMasked_ #-}
 
 -- | Lifted 'M.modifyMVarMasked'.
 modifyMVarMasked :: Concurrent :> es => MVar a -> (a -> Eff es (a, b)) -> Eff es b
 modifyMVarMasked var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.modifyMVarMasked var $ unlift . f
+{-# INLINE modifyMVarMasked #-}
 
 -- | Lifted 'M.mkWeakMVar'.
 mkWeakMVar :: Concurrent :> es => MVar a -> Eff es () -> Eff es (Weak (MVar a))
diff --git a/effectful/src/Effectful/Concurrent/MVar/Strict.hs b/effectful/src/Effectful/Concurrent/MVar/Strict.hs
index 6411515..2d69159 100644
--- a/effectful/src/Effectful/Concurrent/MVar/Strict.hs
+++ b/effectful/src/Effectful/Concurrent/MVar/Strict.hs
@@ -29,6 +29,7 @@ module Effectful.Concurrent.MVar.Strict
   ) where
 
 import System.Mem.Weak (Weak)
+import Control.Exception (evaluate)
 import Control.Concurrent.MVar (MVar)
 import Control.Concurrent.MVar qualified as M
 
@@ -44,7 +45,7 @@ newEmptyMVar = unsafeEff_ M.newEmptyMVar
 
 -- | Lifted 'M.newMVar' that evaluates the value to WHNF.
 newMVar :: Concurrent :> es => a -> Eff es (MVar a)
-newMVar a = unsafeEff_ $ a `seq` M.newMVar a
+newMVar a = unsafeEff_ $ M.newMVar =<< evaluate a
 
 -- | Lifted 'M.takeMVar'.
 takeMVar :: Concurrent :> es => MVar a -> Eff es a
@@ -52,7 +53,7 @@ takeMVar = unsafeEff_ . M.takeMVar
 
 -- | Lifted 'M.putMVar'.
 putMVar :: Concurrent :> es => MVar a -> a -> Eff es ()
-putMVar var a = unsafeEff_ $ a `seq` M.putMVar var a
+putMVar var a = unsafeEff_ $ M.putMVar var =<< evaluate a
 
 -- | Lifted 'M.readMVar'.
 readMVar :: Concurrent :> es => MVar a -> Eff es a
@@ -60,7 +61,7 @@ readMVar = unsafeEff_ . M.readMVar
 
 -- | Lifted 'M.swapMVar' that evaluates the new value to WHNF.
 swapMVar :: Concurrent :> es => MVar a -> a -> Eff es a
-swapMVar var a = unsafeEff_ $ a `seq` M.swapMVar var a
+swapMVar var a = unsafeEff_ $ M.swapMVar var =<< evaluate a
 
 -- | Lifted 'M.tryTakeMVar'.
 tryTakeMVar :: Concurrent :> es => MVar a -> Eff es (Maybe a)
@@ -68,7 +69,7 @@ tryTakeMVar = unsafeEff_ . M.tryTakeMVar
 
 -- | Lifted 'M.tryPutMVar' that evaluates the new value to WHNF.
 tryPutMVar :: Concurrent :> es => MVar a -> a -> Eff es Bool
-tryPutMVar var a = unsafeEff_ $ a `seq` M.tryPutMVar var a
+tryPutMVar var a = unsafeEff_ $ M.tryPutMVar var =<< evaluate a
 
 -- | Lifted 'M.isEmptyMVar'.
 isEmptyMVar :: Concurrent :> es => MVar a -> Eff es Bool
@@ -82,39 +83,45 @@ tryReadMVar = unsafeEff_ . M.tryReadMVar
 withMVar :: Concurrent :> es => MVar a -> (a -> Eff es b) -> Eff es b
 withMVar var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.withMVar var $ unlift . f
+{-# INLINE withMVar #-}
 
 -- | Lifted 'M.withMVarMasked'.
 withMVarMasked :: Concurrent :> es => MVar a -> (a -> Eff es b) -> Eff es b
 withMVarMasked var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.withMVarMasked var $ unlift . f
+{-# INLINE withMVarMasked #-}
 
 -- | Lifted 'M.modifyMVar_' that evaluates the new value to WHNF.
 modifyMVar_ :: Concurrent :> es => MVar a -> (a -> Eff es a) -> Eff es ()
 modifyMVar_ var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.modifyMVar_ var $ \a0 -> do
     a <- unlift $ f a0
-    a `seq` pure a
+    evaluate a
+{-# INLINE modifyMVar_ #-}
 
 -- | Lifted 'M.modifyMVar' that evaluates the new value to WHNF.
 modifyMVar :: Concurrent :> es => MVar a -> (a -> Eff es (a, b)) -> Eff es b
 modifyMVar var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.modifyMVar var $ \a0 -> do
     (a, b) <- unlift $ f a0
-    a `seq` pure (a, b)
+    (, b) <$> evaluate a
+{-# INLINE modifyMVar #-}
 
 -- | Lifted 'M.modifyMVarMasked_' that evaluates the new value to WHNF.
 modifyMVarMasked_ :: Concurrent :> es => MVar a -> (a -> Eff es a) -> Eff es ()
 modifyMVarMasked_ var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.modifyMVarMasked_ var $ \a0 -> do
     a <- unlift $ f a0
-    a `seq` pure a
+    evaluate a
+{-# INLINE modifyMVarMasked_ #-}
 
 -- | Lifted 'M.modifyMVarMasked' that evaluates the new value to WHNF.
 modifyMVarMasked :: Concurrent :> es => MVar a -> (a -> Eff es (a, b)) -> Eff es b
 modifyMVarMasked var f = reallyUnsafeUnliftIO $ \unlift -> do
   M.modifyMVarMasked var $ \a0 -> do
-    a <- unlift $ f a0
-    a `seq` pure a
+    (a, b) <- unlift $ f a0
+    (, b) <$> evaluate a
+{-# INLINE modifyMVarMasked #-}
 
 -- | Lifted 'M.mkWeakMVar'.
 mkWeakMVar :: Concurrent :> es => MVar a -> Eff es () -> Eff es (Weak (MVar a))