diff --git a/reactive-jack.cabal b/reactive-jack.cabal
--- a/reactive-jack.cabal
+++ b/reactive-jack.cabal
@@ -1,12 +1,11 @@
 Name:             reactive-jack
-Version:          0.4
+Version:          0.4.1
 License:          BSD3
 License-File:     LICENSE
 Author:           Henning Thielemann <haskell@henning-thielemann.de>
 Maintainer:       Henning Thielemann <haskell@henning-thielemann.de>
 Homepage:         http://www.haskell.org/haskellwiki/Reactive-balsa
 Category:         Sound, Music
-Build-Type:       Simple
 Synopsis:         Process MIDI events via reactive-banana and JACK
 Description:
    MIDI is the Musical Instrument Digital Interface,
@@ -45,10 +44,7 @@
 Source-Repository this
   type:     darcs
   location: http://hub.darcs.net/thielema/reactive-jack/
-  tag:      0.4
-
-Flag splitBase
-  description: Choose the new smaller, split-up base package.
+  tag:      0.4.1
 
 Library
   Build-Depends:
@@ -62,6 +58,7 @@
     utility-ht >=0.0.8 && <0.1,
     containers >=0.2 && <0.6,
     transformers >=0.2 && <0.6,
+    semigroups >=0.1 && <1.0,
     explicit-exception >=0.1.7 && <0.2,
     extensible-exceptions >=0.1 && <0.2,
     random >=1 && <2,
diff --git a/src/Reactive/Banana/JACK/Common.hs b/src/Reactive/Banana/JACK/Common.hs
--- a/src/Reactive/Banana/JACK/Common.hs
+++ b/src/Reactive/Banana/JACK/Common.hs
@@ -18,8 +18,8 @@
 
 with :: ReaderT Handle (Sync.ExceptionalT JackExc.All IO) () -> IO ()
 with f =
-    Jack.handleExceptions $
-        Jack.withClientDefault "Haskell-MIDI-Filter" $ \c ->
-        Jack.withPort c "input" $ \input ->
-        Jack.withPort c "output" $ \output ->
-        runReaderT f $ Handle c input output
+   Jack.handleExceptions $
+      Jack.withClientDefault "Haskell-MIDI-Filter" $ \c ->
+      Jack.withPort c "input" $ \input ->
+      Jack.withPort c "output" $ \output ->
+      runReaderT f $ Handle c input output
diff --git a/src/Reactive/Banana/JACK/Process.hs b/src/Reactive/Banana/JACK/Process.hs
--- a/src/Reactive/Banana/JACK/Process.hs
+++ b/src/Reactive/Banana/JACK/Process.hs
@@ -39,6 +39,7 @@
 import Data.IORef (IORef, newIORef, readIORef, writeIORef, modifyIORef, )
 import Data.Foldable (forM_, )
 import Data.Monoid (Monoid, mappend, mempty, )
+import Data.Semigroup (Semigroup, (<>), )
 
 import Prelude hiding (sequence, )
 
@@ -81,10 +82,13 @@
 data InEvent =
    InEvent (Map Schedule [Handler AbsoluteTicks]) [MidiMsg.T]
 
+instance Semigroup InEvent where
+   InEvent xs0 ys0 <> InEvent xs1 ys1 =
+      InEvent (Map.unionWith (++) xs0 xs1) (ys0++ys1)
+
 instance Monoid InEvent where
    mempty = InEvent Map.empty []
-   mappend (InEvent xs0 ys0) (InEvent xs1 ys1) =
-      InEvent (Map.unionWith (++) xs0 xs1) (ys0++ys1)
+   mappend = (<>)
 
 inEventBeat :: Acc.T InEvent (Map Schedule [Handler AbsoluteTicks])
 inEventBeat =
@@ -179,6 +183,11 @@
       Map.fromListWith (++) $ EventListAbs.toPairList $
       fmap (:[]) evs
 
+   {-
+   ToDo:
+   How to handle overflow properly?
+   jack.h does not give an advice.
+   -}
    cycleStart <- MT.lift $ Jack.lastFrameTime $ Common.client h
    let cycleStartTicks = absTicksFromNFrames cycleStart
    MT.lift $ writeIORef cycleStartRef cycleStartTicks