diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,7 @@
+0.3.9 [2021.11.01]
+------------------
+* Allow building with GHC 9.2.
+
 0.3.8 [2021.02.17]
 ------------------
 * Add an `IsString CharSet` instance.
diff --git a/charset.cabal b/charset.cabal
--- a/charset.cabal
+++ b/charset.cabal
@@ -1,5 +1,5 @@
 name:          charset
-version:       0.3.8
+version:       0.3.9
 license:       BSD3
 license-File:  LICENSE
 copyright:     (c) Edward Kmett 2010-2012
@@ -26,8 +26,10 @@
    || ==8.2.2
    || ==8.4.4
    || ==8.6.5
-   || ==8.8.3
-   || ==8.10.1
+   || ==8.8.4
+   || ==8.10.7
+   || ==9.0.1
+   || ==9.2.1
 
 source-repository head
   type: git
diff --git a/src/Data/CharSet.hs b/src/Data/CharSet.hs
--- a/src/Data/CharSet.hs
+++ b/src/Data/CharSet.hs
@@ -371,4 +371,6 @@
 
 instance Monoid CharSet where
   mempty = empty
+#if !(MIN_VERSION_base(4,11,0))
   mappend = union
+#endif
diff --git a/src/Data/CharSet/ByteSet.hs b/src/Data/CharSet/ByteSet.hs
--- a/src/Data/CharSet/ByteSet.hs
+++ b/src/Data/CharSet/ByteSet.hs
@@ -32,7 +32,13 @@
 
 import Data.Bits ((.&.), (.|.))
 import Foreign.Storable (peekByteOff, pokeByteOff)
-import GHC.Base (Int(I#), iShiftRA#, narrow8Word#, shiftL#)
+import GHC.Exts ( Int(I#), Word#, iShiftRA#, shiftL#
+#if MIN_VERSION_base(4,16,0)
+                , Word8#, word8ToWord#, wordToWord8#
+#else
+                , narrow8Word#
+#endif
+                )
 import GHC.Word (Word8(W8#))
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Internal as I
@@ -50,7 +56,7 @@
 shiftR (I# x#) (I# i#) = I# (x# `iShiftRA#` i#)
 
 shiftL :: Word8 -> Int -> Word8
-shiftL (W8# x#) (I# i#) = W8# (narrow8Word# (x# `shiftL#` i#))
+shiftL (W8# x#) (I# i#) = W8# (narrow8WordCompat# (word8ToWordCompat# x# `shiftL#` i#))
 
 -- | Convert a bit index to a byte index and bit index inside the byte
 index :: Int -> I
@@ -73,3 +79,17 @@
 member w (ByteSet t) = U.unsafeIndex t byte .&. bit /= 0
   where
     I byte bit = index (fromIntegral w)
+
+#if MIN_VERSION_base(4,16,0)
+word8ToWordCompat# :: Word8# -> Word#
+word8ToWordCompat# = word8ToWord#
+
+narrow8WordCompat# :: Word# -> Word8#
+narrow8WordCompat# = wordToWord8#
+#else
+word8ToWordCompat# :: Word# -> Word#
+word8ToWordCompat# x = x
+
+narrow8WordCompat# :: Word# -> Word#
+narrow8WordCompat# = narrow8Word#
+#endif