diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright Robert Leslie (c) 2017
+Copyright Robert Leslie (c) 2017-2018
 
 All rights reserved.
 
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -8,8 +8,8 @@
   [LMDB]: https://symas.com/lightning-memory-mapped-database/
 
 LMDB is a high-performance [ACID][]-compliant no-maintenance read-optimized
-key-value store. Any Haskell value with a [`Serialise`][Serialise] instance
-can be stored in an LMDB database, or used as a key to index one.
+key-value store. Any Haskell type with a [`Serialise`][Serialise] instance can
+be stored in an LMDB database, or used as a key to index one.
 
   [ACID]: https://en.wikipedia.org/wiki/ACID
   [Serialise]: https://hackage.haskell.org/package/serialise/docs/Codec-Serialise-Tutorial.html#g:3
diff --git a/lmdb-simple.cabal b/lmdb-simple.cabal
--- a/lmdb-simple.cabal
+++ b/lmdb-simple.cabal
@@ -1,6 +1,6 @@
 
 name:                lmdb-simple
-version:             0.3.1.0
+version:             0.4.0.0
 
 synopsis:            Simple API for LMDB
 
@@ -15,7 +15,7 @@
 
 author:              Rob Leslie
 maintainer:          rob@mars.org
-copyright:           © 2017 Robert Leslie
+copyright:           © 2017–2018 Robert Leslie
 
 stability:           experimental
 category:            Database
@@ -43,12 +43,11 @@
   build-depends:       base >= 4.7 && < 5
                      , bytestring >= 0.10 && < 0.11
                      , lmdb >= 0.2 && < 0.3
-                     , serialise >= 0.1 && < 0.2
+                     , serialise >= 0.2 && < 0.3
   ghc-options:         -Wall -Wno-name-shadowing -Wno-unused-do-bind
   default-language:    Haskell2010
   default-extensions:  Trustworthy
   other-extensions:    ConstraintKinds
-                       KindSignatures
                        TypeFamilies
 
 test-suite sample
diff --git a/src/Database/LMDB/Simple.hs b/src/Database/LMDB/Simple.hs
--- a/src/Database/LMDB/Simple.hs
+++ b/src/Database/LMDB/Simple.hs
@@ -4,7 +4,7 @@
 {-|
 Module      : Database.LMDB.Simple
 Description : Simple Haskell API for LMDB
-Copyright   : © 2017 Robert Leslie
+Copyright   : © 2017–2018 Robert Leslie
 License     : BSD3
 Maintainer  : rob@mars.org
 Stability   : experimental
@@ -52,6 +52,7 @@
   , openEnvironment
   , openReadWriteEnvironment
   , openReadOnlyEnvironment
+  , readOnlyEnvironment
   , clearStaleReaders
 
     -- * Transactions
@@ -94,6 +95,10 @@
   , void
   )
 
+import Data.Coerce
+  ( coerce
+  )
+
 import Database.LMDB.Raw
   ( LMDB_Error (LMDB_Error, e_code)
   , MDB_EnvFlag (MDB_NOSUBDIR, MDB_RDONLY)
@@ -211,6 +216,15 @@
 openReadOnlyEnvironment :: FilePath -> Limits -> IO (Environment ReadOnly)
 openReadOnlyEnvironment = openEnvironment
 
+-- | For an LMDB environment opened in 'ReadWrite' mode, return the same
+-- environment restricted to 'ReadOnly' mode. This can be used to prevent
+-- modification of the environment for a subset of an application while
+-- retaining the ability to perform modifications in another subset.
+--
+-- @since 0.4.0.0
+readOnlyEnvironment :: Environment ReadWrite -> Environment ReadOnly
+readOnlyEnvironment = coerce
+
 -- | Check for stale entries in the reader lock table, and return the number
 -- of entries cleared.
 clearStaleReaders :: Environment mode -> IO Int
@@ -284,7 +298,7 @@
           (\e -> let _ = e :: AbortedTransaction in Nothing) Just <$> try io
 
 -- | Explicitly abort the current transaction, nullifying its effects on the
--- LMDB environment. No further actions will be performed within the current
+-- LMDB environment. No further actions will be performed within the
 -- transaction.
 --
 -- In a nested transaction, this causes the child transaction to return
diff --git a/src/Database/LMDB/Simple/Internal.hs b/src/Database/LMDB/Simple/Internal.hs
--- a/src/Database/LMDB/Simple/Internal.hs
+++ b/src/Database/LMDB/Simple/Internal.hs
@@ -1,5 +1,4 @@
 
-{-# LANGUAGE KindSignatures #-}
 {-# LANGUAGE TypeFamilies #-}
 
 module Database.LMDB.Simple.Internal
diff --git a/stack.yaml b/stack.yaml
--- a/stack.yaml
+++ b/stack.yaml
@@ -15,7 +15,7 @@
 # resolver:
 #  name: custom-snapshot
 #  location: "./custom-snapshot.yaml"
-resolver: lts-9.0
+resolver: lts-11.1
 
 # User packages to be built.
 # Various formats can be used as shown in the example below.
@@ -40,13 +40,11 @@
 # Dependency packages to be pulled from upstream that are not in the resolver
 # (e.g., acme-missiles-0.3)
 extra-deps:
-- cborg-0.1.1.0
-- serialise-0.1.0.0
+- cborg-0.2.0.0
+- serialise-0.2.0.0
 
 # Override default flag values for local packages and extra-deps
-flags:
-  serialise:
-    newtime15: true
+flags: {}
 
 # Extra package databases containing global packages
 extra-package-dbs: []
diff --git a/test/Database/LMDB/SimpleSpec.hs b/test/Database/LMDB/SimpleSpec.hs
--- a/test/Database/LMDB/SimpleSpec.hs
+++ b/test/Database/LMDB/SimpleSpec.hs
@@ -27,6 +27,16 @@
       transaction env (put db 50 Nothing >> (,) <$> get db 50 <*> size db)
       `shouldReturn` (Nothing, 99)
 
+    it "correctly serializes non-surrogate chars" $ \(env, db) ->
+      let nonSurrogates = [minBound..'\xD7FF'] ++ ['\xE000'..maxBound] in
+        transaction env (put db 0 (Just nonSurrogates) >> get db 0)
+        `shouldReturn` Just nonSurrogates
+
+    it "correctly serializes surrogate chars" $ \(env, db) ->
+      let surrogates = ['\xD800'..'\xDFFF'] in
+        transaction env (put db 0 (Just surrogates) >> get db 0)
+        `shouldReturn` Just surrogates
+
   describe "transactions" $ do
     it "aborts" $ \(env, db) ->
       ( do transaction env $ put db 0 Nothing