diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000..3550a30
--- /dev/null
+++ b/.envrc
@@ -0,0 +1 @@
+use flake
diff --git a/.travis.yml b/.travis.yml
index 1e67206..1d712c9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -10,12 +10,12 @@ dist: trusty
 language: c
 
 services:
- - redis-server
+  - redis-server
 
 addons:
   apt:
     packages:
-    - libgmp-dev
+      - libgmp-dev
   postgresql: "9.3"
 
 cache:
@@ -25,8 +25,7 @@ cache:
 
 matrix:
   include:
-    - env: STACKARGS="--resolver=lts-11"
-    - env: STACKARGS="--resolver=lts-12"
+    - env: STACKARGS="--resolver=lts-15"
     - env: STACKARGS="--resolver=nightly"
   allow_failures:
     - env: STACKARGS="--resolver=nightly"
diff --git a/examples/serversession-example-yesod-persistent/Model.hs b/examples/serversession-example-yesod-persistent/Model.hs
index cbe20c4..91ab7b5 100644
--- a/examples/serversession-example-yesod-persistent/Model.hs
+++ b/examples/serversession-example-yesod-persistent/Model.hs
@@ -1,3 +1,6 @@
+{-# LANGUAGE DerivingStrategies   #-}
+{-# LANGUAGE StandaloneDeriving   #-}
+{-# LANGUAGE UndecidableInstances #-}
 module Model where
 
 import ClassyPrelude.Yesod
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..b486ac5
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,44 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1619345332,
+        "narHash": "sha256-qHnQkEp1uklKTpx3MvKtY6xzgcqXDsz5nLilbbuL+3A=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "2ebf2558e5bf978c7fb8ea927dfaed8fefab2e28",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "ref": "master",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1620323686,
+        "narHash": "sha256-+gfcE3YTGl+Osc8HzOUXSFO8/0PAK4J8ZxCXZ4hjXHI=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "dfacb8329b2236688b9a1e705116203a213b283a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "master",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..42a5ecf
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,30 @@
+{
+  inputs = {
+    nixpkgs = {
+      type = "github";
+      owner = "NixOS";
+      repo = "nixpkgs";
+      ref = "master";
+    };
+    flake-utils = {
+      type = "github";
+      owner = "numtide";
+      repo = "flake-utils";
+      ref = "master";
+    };
+  };
+
+  outputs = { self, nixpkgs, flake-utils, ... }: flake-utils.lib.eachDefaultSystem
+    (system:
+      let pkgs = import nixpkgs {
+            inherit system;
+            config.allowUnfree = true;
+          };
+      in {
+        devShell = pkgs.mkShell {
+          name = "uni2work-serversession";
+          nativeBuildInputs = with pkgs.haskellPackages; [ stack ];
+        };
+      }
+    );
+}
diff --git a/nixpkgs.nix b/nixpkgs.nix
new file mode 100644
index 0000000..4492a1c
--- /dev/null
+++ b/nixpkgs.nix
@@ -0,0 +1,8 @@
+import (
+  let
+    lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+  in fetchTarball {
+    url = "https://api.github.com/repos/NixOS/nixpkgs/tarball/${lock.nodes.nixpkgs.locked.rev}";
+    sha256 = lock.nodes.nixpkgs.locked.narHash;
+  }
+)
diff --git a/serversession-backend-acid-state/changelog.md b/serversession-backend-acid-state/changelog.md
index e69de29..2de1281 100644
--- a/serversession-backend-acid-state/changelog.md
+++ b/serversession-backend-acid-state/changelog.md
@@ -0,0 +1,3 @@
+# 1.0.4
+
+* bump acid-state to 0.16
diff --git a/serversession-backend-acid-state/serversession-backend-acid-state.cabal b/serversession-backend-acid-state/serversession-backend-acid-state.cabal
index 3252955..096c702 100644
--- a/serversession-backend-acid-state/serversession-backend-acid-state.cabal
+++ b/serversession-backend-acid-state/serversession-backend-acid-state.cabal
@@ -1,5 +1,6 @@
+cabal-version:   >= 1.10
 name:            serversession-backend-acid-state
-version:         1.0.3
+version:         1.0.4
 license:         MIT
 license-file:    LICENSE
 author:          Felipe Lessa <felipe.lessa@gmail.com>
@@ -7,7 +8,6 @@ maintainer:      Michael Xavier <michael@michaelxavier.net>
 synopsis:        Storage backend for serversession using acid-state.
 category:        Web
 stability:       Stable
-cabal-version:   >= 1.8
 build-type:      Simple
 homepage:        https://github.com/yesodweb/serversession
 description:     API docs and the README are available at <http://www.stackage.org/package/serversession-backend-acid-state>
@@ -19,10 +19,11 @@ flag lib-Werror
   manual: True
 
 library
+  default-language: Haskell2010
   hs-source-dirs: src
   build-depends:
       base                      == 4.*
-    , acid-state                == 0.16.*
+    , acid-state                >= 0.16
     , containers
     , mtl
     , safecopy                  >= 0.8 && <0.11
@@ -32,7 +33,7 @@ library
   exposed-modules:
     Web.ServerSession.Backend.Acid
     Web.ServerSession.Backend.Acid.Internal
-  extensions:
+  default-extensions:
     ConstraintKinds
     DeriveDataTypeable
     FlexibleContexts
@@ -47,6 +48,7 @@ library
 
 
 test-suite tests
+  default-language: Haskell2010
   type: exitcode-stdio-1.0
   hs-source-dirs:  tests
   build-depends:
@@ -57,7 +59,7 @@ test-suite tests
     , serversession
     , serversession-backend-acid-state
   main-is:         Main.hs
-  extensions:
+  default-extensions:
     CPP
   ghc-options:     -Wall -threaded "-with-rtsopts=-N -s -M1G -c" -rtsopts
   if flag(lib-Werror)
diff --git a/serversession-backend-acid-state/src/Web/ServerSession/Backend/Acid/Internal.hs b/serversession-backend-acid-state/src/Web/ServerSession/Backend/Acid/Internal.hs
index 57d1412..8fca833 100644
--- a/serversession-backend-acid-state/src/Web/ServerSession/Backend/Acid/Internal.hs
+++ b/serversession-backend-acid-state/src/Web/ServerSession/Backend/Acid/Internal.hs
@@ -109,7 +109,7 @@ instance SafeCopy SS.SessionMap where
 
 -- | We can't @deriveSafeCopy 0 'base ''SS.SessionId@ as
 -- otherwise we'd require an unneeded @SafeCopy sess@.
-instance SafeCopy (SS.SessionId sess) where
+instance Typeable sess => SafeCopy (SS.SessionId sess) where
   putCopy = contain . safePut . SSI.unS
   getCopy = contain $ SSI.S <$> safeGet
   
@@ -118,7 +118,7 @@ instance SafeCopy (SS.SessionId sess) where
 
 -- | We can't @deriveSafeCopy 0 'base ''SS.Session@ due to the
 -- required context.
-instance SafeCopy (SS.Decomposed sess) => SafeCopy (SS.Session sess) where
+instance (Typeable sess, SafeCopy (SS.Decomposed sess)) => SafeCopy (SS.Session sess) where
   putCopy (SS.Session key authId data_ createdAt accessedAt) = contain $ do
     put_t <- getSafePut
     safePut key
@@ -140,7 +140,7 @@ instance SafeCopy (SS.Decomposed sess) => SafeCopy (SS.Session sess) where
 
 -- | We can't @deriveSafeCopy 0 'base ''ServerSessionAcidState@ due
 -- to the required context.
-instance SafeCopy (SS.Decomposed sess) => SafeCopy (ServerSessionAcidState sess) where
+instance (Typeable sess, SafeCopy (SS.Decomposed sess)) => SafeCopy (ServerSessionAcidState sess) where
   putCopy (ServerSessionAcidState sits aits) = contain $ do
     safePut (HM.toList sits)
     safePut (HM.toList aits)
@@ -279,31 +279,27 @@ data DeleteAllSessionsOfAuthId sess = DeleteAllSessionsOfAuthId SS.AuthId derivi
 data InsertSession sess = InsertSession (SS.Session sess) deriving (Typeable)
 data ReplaceSession sess = ReplaceSession (SS.Session sess) deriving (Typeable)
 
-instance SafeCopy (GetSession sess) where
+instance Typeable sess => SafeCopy (GetSession sess) where
   putCopy (GetSession v) = contain $ safePut v
   getCopy = contain $ GetSession <$> safeGet
 
-  errorTypeName _ = "GetSession"
-
-instance SafeCopy (DeleteSession sess) where
+instance Typeable sess => SafeCopy (DeleteSession sess) where
   putCopy (DeleteSession v) = contain $ safePut v
   getCopy = contain $ DeleteSession <$> safeGet
   
   errorTypeName _ = "DeleteSession"
 
-instance SafeCopy (DeleteAllSessionsOfAuthId sess) where
+instance Typeable sess => SafeCopy (DeleteAllSessionsOfAuthId sess) where
   putCopy (DeleteAllSessionsOfAuthId v) = contain $ safePut v
   getCopy = contain $ DeleteAllSessionsOfAuthId <$> safeGet
   
   errorTypeName _ = "DeleteAllSessionsOfAuthId"
 
-instance SafeCopy (SS.Decomposed sess) => SafeCopy (InsertSession sess) where
+instance (Typeable sess, SafeCopy (SS.Decomposed sess)) => SafeCopy (InsertSession sess) where
   putCopy (InsertSession v) = contain $ safePut v
   getCopy = contain $ InsertSession <$> safeGet
 
-  errorTypeName _ = "InsertSession"
-
-instance SafeCopy (SS.Decomposed sess) => SafeCopy (ReplaceSession sess) where
+instance (Typeable sess, SafeCopy (SS.Decomposed sess)) => SafeCopy (ReplaceSession sess) where
   putCopy (ReplaceSession v) = contain $ safePut v
   getCopy = contain $ ReplaceSession <$> safeGet
 
diff --git a/serversession-backend-persistent/changelog.md b/serversession-backend-persistent/changelog.md
index bee723b..41730b8 100644
--- a/serversession-backend-persistent/changelog.md
+++ b/serversession-backend-persistent/changelog.md
@@ -1,3 +1,5 @@
+1.0.5
+* bump persistent to 2.10
 1.0.4
 * Default auth id to NULL to fix a MySQL bug.
 1.0.3
diff --git a/serversession-backend-persistent/serversession-backend-persistent.cabal b/serversession-backend-persistent/serversession-backend-persistent.cabal
index f06080a..b516bfe 100644
--- a/serversession-backend-persistent/serversession-backend-persistent.cabal
+++ b/serversession-backend-persistent/serversession-backend-persistent.cabal
@@ -1,5 +1,6 @@
+cabal-version:   >= 1.10
 name:            serversession-backend-persistent
-version:         1.0.4
+version:         1.0.5
 license:         MIT
 license-file:    LICENSE
 author:          Felipe Lessa <felipe.lessa@gmail.com>
@@ -7,7 +8,6 @@ maintainer:      Michael Xavier <michael@michaelxavier.net>
 synopsis:        Storage backend for serversession using persistent and an RDBMS.
 category:        Web
 stability:       Stable
-cabal-version:   >= 1.8
 build-type:      Simple
 homepage:        https://github.com/yesodweb/serversession
 description:     API docs and the README are available at <http://www.stackage.org/package/serversession-backend-persistent>
@@ -19,6 +19,7 @@ flag lib-Werror
   manual: True
 
 library
+  default-language: Haskell2010
   hs-source-dirs: src
   build-depends:
       base                      == 4.*
@@ -27,7 +28,7 @@ library
     , bytestring
     , cereal                    >= 0.4
     , path-pieces
-    , persistent                >= 2.1
+    , persistent                >= 2.10
     , tagged                    >= 0.7
     , text
     , time
@@ -39,7 +40,7 @@ library
     Web.ServerSession.Backend.Persistent
     Web.ServerSession.Backend.Persistent.Internal.Impl
     Web.ServerSession.Backend.Persistent.Internal.Types
-  extensions:
+  default-extensions:
     DeriveDataTypeable
     EmptyDataDecls
     FlexibleContexts
@@ -62,6 +63,7 @@ library
 
 
 test-suite tests
+  default-language: Haskell2010
   type: exitcode-stdio-1.0
   hs-source-dirs:  tests
   build-depends:
@@ -79,7 +81,7 @@ test-suite tests
 
     , serversession
     , serversession-backend-persistent
-  extensions:
+  default-extensions:
     OverloadedStrings
     TemplateHaskell
   main-is:         Main.hs
diff --git a/serversession-backend-persistent/src/Web/ServerSession/Backend/Persistent/Internal/Impl.hs b/serversession-backend-persistent/src/Web/ServerSession/Backend/Persistent/Internal/Impl.hs
index 623857c..36cc39e 100644
--- a/serversession-backend-persistent/src/Web/ServerSession/Backend/Persistent/Internal/Impl.hs
+++ b/serversession-backend-persistent/src/Web/ServerSession/Backend/Persistent/Internal/Impl.hs
@@ -96,6 +96,7 @@ instance forall sess. P.PersistFieldSql (Decomposed sess) => P.PersistEntity (Pe
         ["Eq", "Ord", "Show", "Typeable"]
         M.mempty
         False
+        Nothing
     where
       pfd :: P.EntityField (PersistentSession sess) typ -> P.FieldDef
       pfd = P.persistFieldDef
@@ -142,8 +143,10 @@ instance forall sess. P.PersistFieldSql (Decomposed sess) => P.PersistEntity (Pe
                  (P.SqlOther "SqlType unset for key")
                  []
                  True
-                 P.NoReference]
+                 P.NoReference
+                 Nothing]
               []))
+        Nothing
   persistFieldDef PersistentSessionKey
     = P.FieldDef
         (P.HaskellName "key")
@@ -153,6 +156,7 @@ instance forall sess. P.PersistFieldSql (Decomposed sess) => P.PersistEntity (Pe
         ["maxlen=30"]
         True
         P.NoReference
+        Nothing
   persistFieldDef PersistentSessionAuthId
     = P.FieldDef
         (P.HaskellName "authId")
@@ -162,6 +166,7 @@ instance forall sess. P.PersistFieldSql (Decomposed sess) => P.PersistEntity (Pe
         ["Maybe", "default=NULL"]
         True
         P.NoReference
+        Nothing
   persistFieldDef PersistentSessionSession
     = P.FieldDef
         (P.HaskellName "session")
@@ -171,6 +176,7 @@ instance forall sess. P.PersistFieldSql (Decomposed sess) => P.PersistEntity (Pe
         []
         True
         P.NoReference
+        Nothing
   persistFieldDef PersistentSessionCreatedAt
     = P.FieldDef
         (P.HaskellName "createdAt")
@@ -180,6 +186,7 @@ instance forall sess. P.PersistFieldSql (Decomposed sess) => P.PersistEntity (Pe
         []
         True
         P.NoReference
+        Nothing
   persistFieldDef PersistentSessionAccessedAt
     = P.FieldDef
         (P.HaskellName "accessedAt")
@@ -189,6 +196,7 @@ instance forall sess. P.PersistFieldSql (Decomposed sess) => P.PersistEntity (Pe
         []
         True
         P.NoReference
+        Nothing
 
   persistIdField = PersistentSessionId
 
diff --git a/serversession-backend-redis/changelog.md b/serversession-backend-redis/changelog.md
index a126c38..ecd3c31 100644
--- a/serversession-backend-redis/changelog.md
+++ b/serversession-backend-redis/changelog.md
@@ -1,3 +1,5 @@
+1.0.4
+* bump hedis to 0.13
 1.0.3
 * Allow hedis-0.10
 1.0.2
diff --git a/serversession-backend-redis/serversession-backend-redis.cabal b/serversession-backend-redis/serversession-backend-redis.cabal
index 7281279..d8d83b1 100644
--- a/serversession-backend-redis/serversession-backend-redis.cabal
+++ b/serversession-backend-redis/serversession-backend-redis.cabal
@@ -1,5 +1,6 @@
+cabal-version:   >= 1.10
 name:            serversession-backend-redis
-version:         1.0.3
+version:         1.0.4
 license:         MIT
 license-file:    LICENSE
 author:          Felipe Lessa <felipe.lessa@gmail.com>
@@ -7,7 +8,6 @@ maintainer:      Michael Xavier <michael@michaelxavier.net>
 synopsis:        Storage backend for serversession using Redis.
 category:        Web
 stability:       Stable
-cabal-version:   >= 1.8
 build-type:      Simple
 homepage:        https://github.com/yesodweb/serversession
 description:     API docs and the README are available at <http://www.stackage.org/package/serversession-backend-redis>
@@ -23,11 +23,12 @@ flag lib-Werror
   manual: True
 
 library
+  default-language: Haskell2010
   hs-source-dirs: src
   build-depends:
       base                      == 4.*
     , bytestring
-    , hedis                     < 0.11
+    , hedis                     < 0.13
     , path-pieces
     , tagged                    >= 0.7
     , text
@@ -43,7 +44,7 @@ library
   exposed-modules:
     Web.ServerSession.Backend.Redis
     Web.ServerSession.Backend.Redis.Internal
-  extensions:
+  default-extensions:
     CPP
     DeriveDataTypeable
     FlexibleContexts
@@ -60,6 +61,7 @@ library
 
 
 test-suite tests
+  default-language: Haskell2010
   type: exitcode-stdio-1.0
   hs-source-dirs:  tests
   build-depends:
diff --git a/serversession-frontend-snap/serversession-frontend-snap.cabal b/serversession-frontend-snap/serversession-frontend-snap.cabal
index 12f9319..58c254a 100644
--- a/serversession-frontend-snap/serversession-frontend-snap.cabal
+++ b/serversession-frontend-snap/serversession-frontend-snap.cabal
@@ -1,3 +1,4 @@
+cabal-version:   >= 1.10
 name:            serversession-frontend-snap
 version:         1.0.1
 license:         MIT
@@ -7,7 +8,6 @@ maintainer:      Michael Xavier <michael@michaelxavier.net>
 synopsis:        Snap bindings for serversession.
 category:        Web
 stability:       Stable
-cabal-version:   >= 1.8
 build-type:      Simple
 homepage:        https://github.com/yesodweb/serversession
 description:     API docs and the README are available at <http://www.stackage.org/package/serversession-frontend-snap>
@@ -20,6 +20,7 @@ flag lib-Werror
 
 
 library
+  default-language: Haskell2010
   hs-source-dirs: src
   build-depends:
       base                      == 4.*
@@ -37,7 +38,7 @@ library
   exposed-modules:
     Web.ServerSession.Frontend.Snap
     Web.ServerSession.Frontend.Snap.Internal
-  extensions:
+  default-extensions:
     DeriveDataTypeable
     FlexibleContexts
     OverloadedStrings
diff --git a/serversession-frontend-wai/serversession-frontend-wai.cabal b/serversession-frontend-wai/serversession-frontend-wai.cabal
index ce4a934..c23b13f 100644
--- a/serversession-frontend-wai/serversession-frontend-wai.cabal
+++ b/serversession-frontend-wai/serversession-frontend-wai.cabal
@@ -1,3 +1,4 @@
+cabal-version:   >= 1.10
 name:            serversession-frontend-wai
 version:         1.0
 license:         MIT
@@ -7,7 +8,6 @@ maintainer:      Michael Xavier <michael@michaelxavier.net>
 synopsis:        wai-session bindings for serversession.
 category:        Web
 stability:       Stable
-cabal-version:   >= 1.8
 build-type:      Simple
 homepage:        https://github.com/yesodweb/serversession
 description:     API docs and the README are available at <http://www.stackage.org/package/serversession-frontend-wai>
@@ -19,6 +19,7 @@ flag lib-Werror
   manual: True
 
 library
+  default-language: Haskell2010
   hs-source-dirs: src
   build-depends:
       base                      >= 4.6   && < 5
@@ -38,7 +39,7 @@ library
   exposed-modules:
     Web.ServerSession.Frontend.Wai
     Web.ServerSession.Frontend.Wai.Internal
-  extensions:
+  default-extensions:
     FlexibleContexts
     OverloadedStrings
     TypeFamilies
diff --git a/serversession-frontend-yesod/serversession-frontend-yesod.cabal b/serversession-frontend-yesod/serversession-frontend-yesod.cabal
index 66e4b1c..821034e 100644
--- a/serversession-frontend-yesod/serversession-frontend-yesod.cabal
+++ b/serversession-frontend-yesod/serversession-frontend-yesod.cabal
@@ -1,3 +1,4 @@
+cabal-version:   >= 1.10
 name:            serversession-frontend-yesod
 version:         1.0
 license:         MIT
@@ -7,7 +8,6 @@ maintainer:      Michael Xavier <michael@michaelxavier.net>
 synopsis:        Yesod bindings for serversession.
 category:        Web
 stability:       Stable
-cabal-version:   >= 1.8
 build-type:      Simple
 homepage:        https://github.com/yesodweb/serversession
 description:     API docs and the README are available at <http://www.stackage.org/package/serversession-frontend-yesod>
@@ -19,6 +19,7 @@ flag lib-Werror
   manual: True
 
 library
+  default-language: Haskell2010
   hs-source-dirs: src
   build-depends:
       base                      == 4.*
@@ -38,7 +39,7 @@ library
   exposed-modules:
     Web.ServerSession.Frontend.Yesod
     Web.ServerSession.Frontend.Yesod.Internal
-  extensions:
+  default-extensions:
     FlexibleContexts
     OverloadedStrings
     TypeFamilies
diff --git a/serversession/changelog.md b/serversession/changelog.md
index e69de29..eac42de 100644
--- a/serversession/changelog.md
+++ b/serversession/changelog.md
@@ -0,0 +1,2 @@
+# 1.0.2
+* add persistent-test to deps
diff --git a/serversession/serversession.cabal b/serversession/serversession.cabal
index e0a38e5..eaba5fe 100644
--- a/serversession/serversession.cabal
+++ b/serversession/serversession.cabal
@@ -1,5 +1,6 @@
+cabal-version:   >= 1.10
 name:            serversession
-version:         1.0.1
+version:         1.0.2
 license:         MIT
 license-file:    LICENSE
 author:          Felipe Lessa <felipe.lessa@gmail.com>
@@ -7,7 +8,6 @@ maintainer:      Michael Xavier <michael@michaelxavier.net>
 synopsis:        Secure, modular server-side sessions.
 category:        Web
 stability:       Stable
-cabal-version:   >= 1.8
 build-type:      Simple
 homepage:        https://github.com/yesodweb/serversession
 description:     API docs and the README are available at <http://www.stackage.org/package/serversession>
@@ -19,16 +19,18 @@ flag lib-Werror
   manual: True
 
 library
+  default-language: Haskell2010
   hs-source-dirs: src
   build-depends:
       base                      == 4.*
     , aeson
-    , base64-bytestring         == 1.0.*
+    , base64-bytestring         >= 1.0 && < 1.3
     , bytestring
     , data-default
     , hashable
     , nonce                     == 1.0.*
     , path-pieces
+    , persistent-test
     , text
     , time
     , transformers
@@ -37,7 +39,7 @@ library
     Web.ServerSession.Core
     Web.ServerSession.Core.Internal
     Web.ServerSession.Core.StorageTests
-  extensions:
+  default-extensions:
     DeriveDataTypeable
     FlexibleContexts
     OverloadedStrings
@@ -53,6 +55,7 @@ library
 
 
 test-suite tests
+  default-language: Haskell2010
   type: exitcode-stdio-1.0
   hs-source-dirs:  tests
   build-depends:
@@ -64,7 +67,7 @@ test-suite tests
     , hspec                     >= 2.1 && < 3
     , QuickCheck
     , serversession
-  extensions:
+  default-extensions:
     DeriveDataTypeable
     FlexibleContexts
     OverloadedStrings
diff --git a/serversession/src/Web/ServerSession/Core/StorageTests.hs b/serversession/src/Web/ServerSession/Core/StorageTests.hs
index 875d1b1..b7e7fda 100644
--- a/serversession/src/Web/ServerSession/Core/StorageTests.hs
+++ b/serversession/src/Web/ServerSession/Core/StorageTests.hs
@@ -10,6 +10,7 @@ module Web.ServerSession.Core.StorageTests
 import Control.Applicative as A
 import Control.Exception (Exception)
 import Control.Monad
+import DataTypeTest (roundUTCTime)
 import Web.ServerSession.Core.Internal
 
 import qualified Crypto.Nonce as N
@@ -173,8 +174,8 @@ allStorageTests storage it runIO parallel _shouldBe shouldReturn shouldThrow = d
               { sessionKey        = sid
               , sessionAuthId     = Nothing
               , sessionData       = SessionMap $ HM.fromList vals
-              , sessionCreatedAt  = now
-              , sessionAccessedAt = now
+              , sessionCreatedAt  = roundUTCTime now
+              , sessionAccessedAt = roundUTCTime now
               }
             ver2 = session { sessionData = SessionMap HM.empty }
         run (getSession storage sid) `shouldReturn` Nothing
@@ -223,8 +224,8 @@ generateSession gen hasAuthId = do
     { sessionKey        = sid
     , sessionAuthId     = authId
     , sessionData       = SessionMap data_
-    , sessionCreatedAt  = TI.addUTCTime (-1000) now
-    , sessionAccessedAt = now
+    , sessionCreatedAt  = roundUTCTime $ TI.addUTCTime (-1000) now
+    , sessionAccessedAt = roundUTCTime $ now
     }
 
 data HasAuthId = HasAuthId | NoAuthId
diff --git a/stack.nix b/stack.nix
new file mode 100644
index 0000000..762fd74
--- /dev/null
+++ b/stack.nix
@@ -0,0 +1,16 @@
+{ ghc, nixpkgs ? import ./nixpkgs.nix }:
+
+let
+  # haskellPackages = import ./stackage.nix { inherit nixpkgs; };
+  haskellPackages = pkgs.haskellPackages;
+  inherit (nixpkgs {}) pkgs;
+in pkgs.haskell.lib.buildStackProject {
+  inherit ghc;
+  inherit (haskellPackages) stack;
+  name = "stackenv";
+  buildInputs = (with pkgs;
+    [ postgresql zlib libsodium gmp llvm_9
+    ]) ++ (with haskellPackages;
+    [ yesod-bin happy alex
+    ]);
+}
diff --git a/stack.yaml b/stack.yaml
index 9a431b3..63c39c1 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,4 +1,18 @@
-resolver: lts-15.0
+flags:
+  serversession-backend-acid-state:
+    lib-Werror: true
+  serversession-frontend-wai:
+    lib-Werror: true
+  serversession-backend-persistent:
+    lib-Werror: true
+  serversession:
+    lib-Werror: true
+  serversession-backend-redis:
+    lib-Werror: true
+  serversession-frontend-yesod:
+    lib-Werror: true
+  serversession-frontend-snap:
+    lib-Werror: true
 packages:
   - serversession
   - serversession-backend-acid-state
@@ -8,25 +22,16 @@ packages:
   - serversession-frontend-wai
   - serversession-frontend-yesod
   - examples/serversession-example-yesod-persistent
-flags:
-  serversession:
-    lib-Werror: true
-  serversession-backend-acid-state:
-    lib-Werror: true
-  serversession-backend-persistent:
-    lib-Werror: true
-  serversession-backend-redis:
-    lib-Werror: true
-  serversession-frontend-snap:
-    lib-Werror: true
-  serversession-frontend-wai:
-    lib-Werror: true
-  serversession-frontend-yesod:
-    lib-Werror: true
 extra-deps:
-  - acid-state-0.16.0
-  - snap-1.1.1.0
-  - heist-1.1
-  - map-syntax-0.3
-  - pwstore-fast-2.4.4
-  - xmlhtml-0.2.5.2
+  - snap-1.1.3.0@sha256:0c0814d2ab1c3d5f22cef4615b2913ded18e87710ea6febdbe6e3ab8d9838735,8872
+  - acid-state-0.16.0@sha256:a5640fd8d99bdb5f152476a2ae56cc8eb81864b280c8ec7d1387e81296ed844d,6190
+  - heist-1.1.0.1@sha256:7355cf8c1a7ef84c0c800c0539f7b99e7e540cace697238009a2dea1f05231f1,9311
+  - map-syntax-0.3@sha256:ca8b449615fa57419c16a5e98844624a6ac758692b87b3cfae8c74c87c56f1b2,2420
+  - pwstore-fast-2.4.4@sha256:9b6a37510d8b9f37f409a8ab3babac9181afcaaa3fce8ba1c131a7ed3de30698,1351
+  - xmlhtml-0.2.5.2@sha256:3f0990f725551985d777e8edb5563fe99aee998f1fde6a7633f720f76df54701,46997
+resolver: lts-16.31
+nix:
+  packages: []
+  pure: false
+  shell-file: ./stack.nix
+  add-gc-roots: true
diff --git a/stack.yaml.lock b/stack.yaml.lock
index fa6d85a..603b6fd 100644
--- a/stack.yaml.lock
+++ b/stack.yaml.lock
@@ -4,51 +4,51 @@
 #   https://docs.haskellstack.org/en/stable/lock_files
 
 packages:
+- completed:
+    hackage: snap-1.1.3.0@sha256:0c0814d2ab1c3d5f22cef4615b2913ded18e87710ea6febdbe6e3ab8d9838735,8872
+    pantry-tree:
+      size: 5743
+      sha256: 804f55a8cab81e720547308e799243e81f43e089b860c0d3160a938cad86ed0d
+  original:
+    hackage: snap-1.1.3.0@sha256:0c0814d2ab1c3d5f22cef4615b2913ded18e87710ea6febdbe6e3ab8d9838735,8872
 - completed:
     hackage: acid-state-0.16.0@sha256:a5640fd8d99bdb5f152476a2ae56cc8eb81864b280c8ec7d1387e81296ed844d,6190
     pantry-tree:
       size: 13678
       sha256: c6e4b7f00d2a500e6286beafe3a2da7ba898a9ea31f5744df57cdce8a8f5890f
   original:
-    hackage: acid-state-0.16.0
+    hackage: acid-state-0.16.0@sha256:a5640fd8d99bdb5f152476a2ae56cc8eb81864b280c8ec7d1387e81296ed844d,6190
 - completed:
-    hackage: snap-1.1.1.0@sha256:3b6301b66f244074d1d7a87173cc70871df1df84b3a86bba5e996422d5e73f45,9093
-    pantry-tree:
-      size: 5743
-      sha256: 23a8899b96ab2dd080328b35f047c057c06ff1dc31a73b724a7a69ba3f5db374
-  original:
-    hackage: snap-1.1.1.0
-- completed:
-    hackage: heist-1.1@sha256:20187de15ef630f8f6debc1cc22cacefb55ddf8864749294bfe2b79a831cad8d,8722
+    hackage: heist-1.1.0.1@sha256:7355cf8c1a7ef84c0c800c0539f7b99e7e540cace697238009a2dea1f05231f1,9311
     pantry-tree:
       size: 7354
-      sha256: 977c0818628cc92775afbf063032e308e55e29e85eaf6289e955dcdcd80b563f
+      sha256: a2635ed49de6debaf8b98189989f83ab58dcc125c6ae8e57f6fe0903bc7fa8ff
   original:
-    hackage: heist-1.1
+    hackage: heist-1.1.0.1@sha256:7355cf8c1a7ef84c0c800c0539f7b99e7e540cace697238009a2dea1f05231f1,9311
 - completed:
     hackage: map-syntax-0.3@sha256:ca8b449615fa57419c16a5e98844624a6ac758692b87b3cfae8c74c87c56f1b2,2420
     pantry-tree:
       size: 558
       sha256: c196bee0433f9540e4251ebd1be06d802ff7cc4931e6f0aedc38babd28683a3c
   original:
-    hackage: map-syntax-0.3
+    hackage: map-syntax-0.3@sha256:ca8b449615fa57419c16a5e98844624a6ac758692b87b3cfae8c74c87c56f1b2,2420
 - completed:
     hackage: pwstore-fast-2.4.4@sha256:9b6a37510d8b9f37f409a8ab3babac9181afcaaa3fce8ba1c131a7ed3de30698,1351
     pantry-tree:
       size: 270
       sha256: ff4a44ede62515efe5cd366a5803f7183c811c4a0cf56eea88da94181c4844c0
   original:
-    hackage: pwstore-fast-2.4.4
+    hackage: pwstore-fast-2.4.4@sha256:9b6a37510d8b9f37f409a8ab3babac9181afcaaa3fce8ba1c131a7ed3de30698,1351
 - completed:
     hackage: xmlhtml-0.2.5.2@sha256:3f0990f725551985d777e8edb5563fe99aee998f1fde6a7633f720f76df54701,46997
     pantry-tree:
       size: 61835
       sha256: bb1bd95db3738e18d112bbc9724510ee64a51b7eda61494507f4957c5e2281f6
   original:
-    hackage: xmlhtml-0.2.5.2
+    hackage: xmlhtml-0.2.5.2@sha256:3f0990f725551985d777e8edb5563fe99aee998f1fde6a7633f720f76df54701,46997
 snapshots:
 - completed:
-    size: 488576
-    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/15/0.yaml
-    sha256: e4b6a87b47ec1cf63a7f1a0884a3b276fce2b0d174a10e8753c4f618e7983568
-  original: lts-15.0
+    size: 534126
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/16/31.yaml
+    sha256: 637fb77049b25560622a224845b7acfe81a09fdb6a96a3c75997a10b651667f6
+  original: lts-16.31