diff --git a/MemoTrie.cabal b/MemoTrie.cabal
--- a/MemoTrie.cabal
+++ b/MemoTrie.cabal
@@ -1,5 +1,5 @@
 Name:                MemoTrie
-Version:             0.6.8
+Version:             0.6.9
 Cabal-Version:       >= 1.10
 Synopsis:            Trie-based memo functions
 Category:            Data
diff --git a/src/Data/MemoTrie.hs b/src/Data/MemoTrie.hs
--- a/src/Data/MemoTrie.hs
+++ b/src/Data/MemoTrie.hs
@@ -587,7 +587,12 @@
 
 instance (HasTrie a, Monoid b) => Monoid (a :->: b) where
   mempty  = trie mempty
+#if !MIN_VERSION_base(4,11,0)
   mappend = inTrie2 mappend
+#else
+instance (HasTrie a, Semigroup b) => Semigroup (a :->: b) where
+  (<>)    = inTrie2 (<>)
+#endif
 
 instance HasTrie a => Functor ((:->:) a) where
   fmap f = inTrie (fmap f)