diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 0.4.1.0
+
+* Add `MonadFix` instance for `Eff`, thanks to Adriaan Leijnse
+
 # 0.4.0.0
 
 * Move `mapHandle` out of class `Handle`
diff --git a/bluefin-internal.cabal b/bluefin-internal.cabal
--- a/bluefin-internal.cabal
+++ b/bluefin-internal.cabal
@@ -1,6 +1,6 @@
 cabal-version:      3.0
 name:               bluefin-internal
-version:            0.4.0.0
+version:            0.4.1.0
 license:            MIT
 license-file:       LICENSE
 author:             Tom Ellis
diff --git a/src/Bluefin/Internal.hs b/src/Bluefin/Internal.hs
--- a/src/Bluefin/Internal.hs
+++ b/src/Bluefin/Internal.hs
@@ -26,6 +26,7 @@
 import Control.Exception qualified
 import Control.Monad (forever)
 import Control.Monad.Base (MonadBase (liftBase))
+import Control.Monad.Fix (MonadFix)
 import Control.Monad.IO.Class (MonadIO, liftIO)
 import Control.Monad.IO.Unlift (MonadUnliftIO, withRunInIO)
 import Control.Monad.Trans.Control (MonadBaseControl, StM, liftBaseWith, restoreM)
@@ -53,7 +54,7 @@
 
 newtype Eff (es :: Effects) a = UnsafeMkEff {unsafeUnEff :: IO a}
   deriving stock (Functor)
-  deriving newtype (Applicative, Monad)
+  deriving newtype (Applicative, Monad, MonadFix)
 
 type role Eff nominal representational