diff --git a/sourcemap.cabal b/sourcemap.cabal
--- a/sourcemap.cabal
+++ b/sourcemap.cabal
@@ -1,5 +1,5 @@
 name:                sourcemap
-version:             0.1.5
+version:             0.1.6
 synopsis:            Implementation of source maps as proposed by Google and Mozilla.
 description:         Implementation of source maps, revision 3, proposed by Google and Mozilla here
                      <https://wiki.mozilla.org/DevTools/Features/SourceMap> and here
diff --git a/src/SourceMap.hs b/src/SourceMap.hs
--- a/src/SourceMap.hs
+++ b/src/SourceMap.hs
@@ -90,7 +90,7 @@
              result += VLQ.encode (indexOf name names - previousName)
              return (indexOf name names)
     -- Return the byte buffer.
-    toLazyByteString <$> readSTRef result
+    fmap toLazyByteString $ readSTRef result
 
   updating r f = readSTRef r >>= \x -> f x >>= writeSTRef r
   r += y = modifySTRef r (<> lazyByteString y)