diff --git a/Changelog.md b/Changelog.md
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,3 +1,11 @@
+# 1.2.6
+
+## Other Changes
+
+* Increased upper bound of `base` and support GHC 8.4.
+
+---
+
 # 1.2.5
 
 ## Other Changes
diff --git a/logging-effect.cabal b/logging-effect.cabal
--- a/logging-effect.cabal
+++ b/logging-effect.cabal
@@ -1,5 +1,5 @@
 name: logging-effect
-version: 1.2.5
+version: 1.2.6
 synopsis: A mtl-style monad transformer for general purpose & compositional logging
 homepage: https://github.com/ocharles/logging-effect
 license: BSD3
@@ -13,7 +13,7 @@
 library
   exposed-modules:     Control.Monad.Log
   other-extensions:    ViewPatterns, OverloadedStrings, GeneralizedNewtypeDeriving, FlexibleContexts, FlexibleInstances, MultiParamTypeClasses, FunctionalDependencies, PatternSynonyms
-  build-depends:       base >=4.8 && <4.11
+  build-depends:       base >=4.8 && <4.12
                      , async >=2.0 && <2.3
                      , transformers >=0.4 && <0.6
                      , text >=1.2 && <1.3
diff --git a/src/Control/Monad/Log.hs b/src/Control/Monad/Log.hs
--- a/src/Control/Monad/Log.hs
+++ b/src/Control/Monad/Log.hs
@@ -91,7 +91,7 @@
 import Control.Monad.Trans.Reader (ReaderT(..))
 import Control.Monad.Trans.State.Strict (StateT(..))
 import Control.Monad.Writer.Class (MonadWriter(..))
-import Data.Monoid
+import Data.Semigroup
 import Data.Time (UTCTime, getCurrentTime)
 #if !MIN_VERSION_base(4, 9, 0)
 import GHC.SrcLoc (SrcLoc, showSrcLoc)
@@ -100,6 +100,7 @@
 import GHC.Stack (SrcLoc, CallStack, getCallStack, prettySrcLoc)
 #endif
 import System.IO (Handle, hFlush)
+import GHC.IO.Handle.FD (stdin, stdout, stderr)
 import qualified Data.Text.Lazy as LT
 import qualified Text.PrettyPrint.Leijen.Text as PP
 import qualified Data.List.NonEmpty as NEL
@@ -399,11 +400,17 @@
 
 newtype Ap m = Ap { runAp :: m () }
 
+instance Applicative m => Semigroup (Ap m) where
+  Ap l <> Ap r = Ap (l *> r)
+  {-# INLINEABLE (<>) #-}
+
 instance Applicative m => Monoid (Ap m) where
   mempty = Ap (pure ())
   {-# INLINEABLE mempty #-}
+#if !(MIN_VERSION_base(4,11,0))
   Ap l `mappend` Ap r = Ap (l *> r)
   {-# INLINEABLE mappend #-}
+#endif
 
 -- | The main instance of 'MonadLog', which replaces calls to 'logMessage' with calls to a 'Handler'.
 instance Monad m => MonadLog message (LoggingT message m) where
@@ -571,7 +578,7 @@
   MkPureLoggingT
     (StateT (\s ->
                do (a,l) <- m
-                  return (a,s <> l)))
+                  return (a,mappend s l)))
 {-# INLINEABLE mkPureLoggingT #-}
 
 instance MonadTrans (PureLoggingT log) where