diff --git a/src/Synthesizer/Dimensional/Process.hs b/src/Synthesizer/Dimensional/Process.hs
--- a/src/Synthesizer/Dimensional/Process.hs
+++ b/src/Synthesizer/Dimensional/Process.hs
@@ -73,7 +73,6 @@
    (<*>) = apply
 
 instance Monad (T s u t) where
-   return = pure
    (>>=)  = bind
 
 instance MonadFix (T s u t) where
diff --git a/src/Synthesizer/Dimensional/Rate/Dirac.hs b/src/Synthesizer/Dimensional/Rate/Dirac.hs
--- a/src/Synthesizer/Dimensional/Rate/Dirac.hs
+++ b/src/Synthesizer/Dimensional/Rate/Dirac.hs
@@ -46,7 +46,6 @@
 
 instance Mn.Monoid (sig Bool) => Mn.Monoid (T s sig) where
    mempty = Cons Mn.mempty
-   mappend (Cons x) (Cons y) = Cons (Mn.mappend x y)
 
 instance Cut.Consume (sig Bool) => Cut.Consume (T s sig) where
    {-# INLINE null #-}
diff --git a/synthesizer-dimensional.cabal b/synthesizer-dimensional.cabal
--- a/synthesizer-dimensional.cabal
+++ b/synthesizer-dimensional.cabal
@@ -1,5 +1,5 @@
 Name:           synthesizer-dimensional
-Version:        0.9
+Version:        0.9.0.1
 License:        GPL
 License-File:   LICENSE
 Author:         Henning Thielemann <haskell@henning-thielemann.de>
@@ -33,7 +33,7 @@
   Location:    http://code.haskell.org/synthesizer/dimensional/
 
 Source-Repository this
-  Tag:         0.9
+  Tag:         0.9.0.1
   Type:        darcs
   Location:    http://code.haskell.org/synthesizer/dimensional/
 
@@ -51,7 +51,7 @@
     bytestring >= 0.9 && <0.13,
     random >=1.0 && <1.4,
     utility-ht >=0.0.13 && <0.1,
-    base >= 4 && <5
+    base >= 4.11 && <5
 
   If impl(ghc>=7.0)
     GHC-Options: -fwarn-unused-do-bind