diff --git a/monoidal-containers.cabal b/monoidal-containers.cabal
--- a/monoidal-containers.cabal
+++ b/monoidal-containers.cabal
@@ -1,5 +1,5 @@
 name:                monoidal-containers
-version:             0.3.0.2
+version:             0.3.1.0
 synopsis:            Containers with monoidal accumulation
 description:
     Containers with merging via monoidal accumulation. The 'Monoid' instances
@@ -23,7 +23,7 @@
 category:            Data
 build-type:          Simple
 cabal-version:       >=1.10
-tested-with:         GHC ==7.6.3, GHC ==7.8.4, GHC ==8.0.1
+tested-with:         GHC ==7.6.3, GHC ==7.8.4, GHC ==8.0.2, GHC ==8.2.2, GHC ==8.4.1
 
 source-repository head
   type:                git
@@ -38,12 +38,13 @@
                        GeneralizedNewtypeDeriving,
                        DeriveTraversable,
                        DeriveDataTypeable
-  build-depends:       base >=4.5 && <4.11,
+  build-depends:       base >=4.5 && <4.12,
                        containers >=0.5 && <0.6,
                        deepseq >=1.3 && <1.5,
                        unordered-containers >= 0.2 && < 0.3,
                        hashable >= 1.2 && < 1.3,
                        lens >=4.4 && <5,
-                       newtype >=0.2 && <0.3
+                       newtype >=0.2 && <0.3,
+                       semigroups >= 0.18 && < 0.19
   hs-source-dirs:      src
   default-language:    Haskell2010
diff --git a/src/Data/HashMap/Monoidal.hs b/src/Data/HashMap/Monoidal.hs
--- a/src/Data/HashMap/Monoidal.hs
+++ b/src/Data/HashMap/Monoidal.hs
@@ -38,7 +38,7 @@
 
 import Prelude hiding (lookup, map)
 import Data.Maybe (fromMaybe)
-import Data.Monoid
+import Data.Semigroup
 import Data.Foldable (Foldable)
 import Control.Applicative (pure)
 import Data.Data (Data)
@@ -92,11 +92,17 @@
     _Wrapped' = iso unpack pack
     {-# INLINE _Wrapped' #-}
 
+instance (Eq k, Hashable k, Semigroup a) => Semigroup (MonoidalHashMap k a) where
+    MonoidalHashMap a <> MonoidalHashMap b = MonoidalHashMap $ M.unionWith (<>) a b
+    {-# INLINE (<>) #-}
+
 instance (Eq k, Hashable k, Monoid a) => Monoid (MonoidalHashMap k a) where
     mempty = MonoidalHashMap mempty
     {-# INLINE mempty #-}
-    MonoidalHashMap a `mappend` MonoidalHashMap b = MonoidalHashMap $ M.unionWith mappend a b
+#if !(MIN_VERSION_base(4,11,0))
+    mappend (MonoidalHashMap a) (MonoidalHashMap b) = MonoidalHashMap $ M.unionWith mappend a b
     {-# INLINE mappend #-}
+#endif
 
 instance Newtype (MonoidalHashMap k a) (M.HashMap k a) where
     pack = MonoidalHashMap
diff --git a/src/Data/Map/Monoidal.hs b/src/Data/Map/Monoidal.hs
--- a/src/Data/Map/Monoidal.hs
+++ b/src/Data/Map/Monoidal.hs
@@ -28,7 +28,7 @@
     , keys
     ) where
 
-import Data.Monoid
+import Data.Semigroup
 import Data.Foldable (Foldable)
 import Data.Traversable (Traversable)
 import Control.Applicative (Applicative, pure)
@@ -89,11 +89,17 @@
     _Wrapped' = iso unpack pack
     {-# INLINE _Wrapped' #-}
 
+instance (Ord k, Semigroup a) => Semigroup (MonoidalMap k a) where
+    MonoidalMap a <> MonoidalMap b = MonoidalMap $ M.unionWith (<>) a b
+    {-# INLINE (<>) #-}
+
 instance (Ord k, Monoid a) => Monoid (MonoidalMap k a) where
     mempty = MonoidalMap mempty
     {-# INLINE mempty #-}
-    MonoidalMap a `mappend` MonoidalMap b = MonoidalMap $ M.unionWith mappend a b
+#if !(MIN_VERSION_base(4,11,0))
+    mappend (MonoidalMap a) (MonoidalMap b) = MonoidalMap $ M.unionWith mappend a b
     {-# INLINE mappend #-}
+#endif
 
 instance Newtype (MonoidalMap k a) (M.Map k a) where
     pack = MonoidalMap
diff --git a/src/Data/Map/Monoidal/Strict.hs b/src/Data/Map/Monoidal/Strict.hs
--- a/src/Data/Map/Monoidal/Strict.hs
+++ b/src/Data/Map/Monoidal/Strict.hs
@@ -28,7 +28,7 @@
     , keys
     ) where
 
-import Data.Monoid
+import Data.Semigroup
 import Data.Foldable (Foldable)
 import Data.Traversable (Traversable)
 import Control.Applicative (Applicative, pure)
@@ -89,11 +89,17 @@
     _Wrapped' = iso unpack pack
     {-# INLINE _Wrapped' #-}
 
-instance (Ord k, Monoid a) => Monoid (MonoidalMap k a) where
+instance (Ord k, Semigroup a) => Semigroup (MonoidalMap k a) where
+    MonoidalMap a <> MonoidalMap b = MonoidalMap $ M.unionWith (<>) a b
+    {-# INLINE (<>) #-}
+
+instance (Ord k, Semigroup a, Monoid a) => Monoid (MonoidalMap k a) where
     mempty = MonoidalMap mempty
     {-# INLINE mempty #-}
-    MonoidalMap a `mappend` MonoidalMap b = MonoidalMap $ M.unionWith mappend a b
+#if !(MIN_VERSION_base(4,11,0))
+    mappend (MonoidalMap a) (MonoidalMap b) = MonoidalMap $ M.unionWith mappend a b
     {-# INLINE mappend #-}
+#endif
 
 instance Newtype (MonoidalMap k a) (M.Map k a) where
     pack = MonoidalMap