diff --git a/example/Domino.hs b/example/Domino.hs
--- a/example/Domino.hs
+++ b/example/Domino.hs
@@ -37,7 +37,7 @@
 import qualified Data.Set as Set
 import Control.Applicative (pure)
 import Data.Set (Set)
-import Data.Monoid (Monoid, mempty, mappend, mconcat)
+import Data.Monoid (Monoid, mempty, mconcat)
 import Data.Semigroup (Semigroup, (<>))
 
 
@@ -67,7 +67,6 @@
 
 instance Monoid Borders where
    mempty = Borders mempty mempty
-   mappend = (<>)
 
 
 above, left :: Position -> Position
diff --git a/set-cover.cabal b/set-cover.cabal
--- a/set-cover.cabal
+++ b/set-cover.cabal
@@ -1,6 +1,6 @@
 Cabal-Version:    2.2
 Name:             set-cover
-Version:          0.1.2
+Version:          0.1.2.1
 License:          BSD-3-Clause
 License-File:     LICENSE
 Author:           Henning Thielemann, Helmut Podhaisky
@@ -48,7 +48,7 @@
   Default:     False
 
 Source-Repository this
-  Tag:         0.1.2
+  Tag:         0.1.2.1
   Type:        darcs
   Location:    https://hub.darcs.net/thielema/set-cover/
 
@@ -67,7 +67,7 @@
     semigroups >=0.1 && <1,
     utility-ht >=0.0.12 && <0.1,
     prelude-compat ==0.*,
-    base >=4 && <5
+    base >=4.11 && <5
 
   Default-Language: Haskell98
   GHC-Options:      -Wall
diff --git a/src/Math/SetCover/BitMap.hs b/src/Math/SetCover/BitMap.hs
--- a/src/Math/SetCover/BitMap.hs
+++ b/src/Math/SetCover/BitMap.hs
@@ -15,7 +15,7 @@
 
 import qualified Data.List.Reverse.StrictSpine as ListRev
 import qualified Data.List as List
-import Data.Monoid (Monoid, mempty, mappend)
+import Data.Monoid (Monoid, mempty)
 import Data.Semigroup (Semigroup, (<>))
 import Data.Tuple.HT (mapSnd, swap)
 
@@ -30,7 +30,6 @@
 
 instance (Bit.C bits) => Monoid (Map bits) where
    mempty = Map []
-   mappend = add
 
 
 fromSet :: Bit.C bits => Set bits -> Map bits
diff --git a/src/Math/SetCover/BitSet.hs b/src/Math/SetCover/BitSet.hs
--- a/src/Math/SetCover/BitSet.hs
+++ b/src/Math/SetCover/BitSet.hs
@@ -3,7 +3,7 @@
 import qualified Math.SetCover.Bit as Bit
 import Math.SetCover.Bit ((.|.), (.&.))
 
-import Data.Monoid (Monoid, mempty, mappend)
+import Data.Monoid (Monoid, mempty)
 import Data.Semigroup (Semigroup, (<>))
 
 
@@ -14,7 +14,6 @@
 
 instance (Bit.C bits) => Monoid (Set bits) where
    mempty = empty
-   mappend = (<>)
 
 empty :: Bit.C bits => Set bits
 empty = Set Bit.empty