diff --git a/bin/ic-ref-run.hs b/bin/ic-ref-run.hs
index d6cd7b8d..31991b81 100644
--- a/bin/ic-ref-run.hs
+++ b/bin/ic-ref-run.hs
@@ -21,7 +21,7 @@ import qualified Data.ByteString.Lazy.Char8 as BC
 import qualified Data.ByteString.Builder as B
 import qualified Data.Text as T
 import Control.Monad.Trans
-import Control.Monad.Trans.State
+import Control.Monad.Trans.State.Strict
 import Text.Printf
 import Data.List
 import Prettyprinter (pretty)
diff --git a/default.nix b/default.nix
index 7b9f0462..b9d0a097 100644
--- a/default.nix
+++ b/default.nix
@@ -39,16 +39,21 @@ let staticHaskellPackages = nixpkgs.pkgsStatic.haskellPackages.override {
 }; in
 
 let
-  ic-hs = nixpkgs.haskell.lib.dontCheck (
-    haskellPackages.ic-hs.overrideAttrs (old: {
+  ic-hs =
+    let
+      ic-hs-pkg =
+        nixpkgs.haskell.lib.disableLibraryProfiling
+          (nixpkgs.haskell.lib.disableExecutableProfiling
+            (nixpkgs.haskell.lib.dontCheck haskellPackages.ic-hs));
+    in
+    ic-hs-pkg.overrideAttrs (old: {
       installPhase = (old.installPhase or "") + ''
         mkdir $out/test-data
         cp ${universal-canister}/universal-canister.wasm $out/test-data
       '';
       # variant of justStaticExecutables that retains propagatedBuildInputs
       postFixup = "rm -rf $out/lib $out/share/doc";
-    })
-  );
+    });
 
   # Alias, to be replaced with a derivation that just copies bin/ic-ref
   ic-ref = ic-hs;
diff --git a/ic-hs.cabal b/ic-hs.cabal
index d19aa988..e488aa78 100644
--- a/ic-hs.cabal
+++ b/ic-hs.cabal
@@ -9,7 +9,7 @@ extra-source-files:  cbits/*.h ic.did
 
 common ghc-flags
   default-language:    Haskell2010
-  ghc-options:         -Wall -Wno-name-shadowing
+  ghc-options:         -Wall -Wno-name-shadowing -O2
 
 library
   import: ghc-flags
@@ -187,7 +187,7 @@ library
 
 executable ic-ref
   import: ghc-flags
-  ghc-options: -rtsopts
+  ghc-options: -rtsopts -threaded
 
   hs-source-dirs: bin
   main-is: ic-ref.hs
@@ -204,7 +204,7 @@ executable ic-ref
 
 executable ic-ref-run
   import: ghc-flags
-  ghc-options: -rtsopts
+  ghc-options: -rtsopts -threaded
 
   hs-source-dirs: bin
   main-is: ic-ref-run.hs
@@ -226,7 +226,7 @@ executable ic-ref-run
 
 executable ic-ref-test
   import: ghc-flags
-  ghc-options: -rtsopts
+  ghc-options: -rtsopts -threaded
 
   hs-source-dirs: bin
   main-is: ic-ref-test.hs
diff --git a/src/IC/Canister.hs b/src/IC/Canister.hs
index 8a821255..4bb5a0a3 100644
--- a/src/IC/Canister.hs
+++ b/src/IC/Canister.hs
@@ -3,6 +3,7 @@
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE StrictData #-}
 
 module IC.Canister
     ( WasmState
diff --git a/src/IC/Canister/Imp.hs b/src/IC/Canister/Imp.hs
index 43aa0344..e0089387 100644
--- a/src/IC/Canister/Imp.hs
+++ b/src/IC/Canister/Imp.hs
@@ -6,6 +6,7 @@
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE NumericUnderscores #-}
+{-# LANGUAGE StrictData #-}
 
 {-|
 The canister interface, presented imperatively (or impurely), i.e. without rollback
diff --git a/src/IC/Canister/Snapshot.hs b/src/IC/Canister/Snapshot.hs
index 7dc02c29..828c7d6e 100644
--- a/src/IC/Canister/Snapshot.hs
+++ b/src/IC/Canister/Snapshot.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE StrictData #-}
 
 {-# OPTIONS_GHC -Wno-orphans #-}
 module IC.Canister.Snapshot ( CanisterSnapshot(..) ) where
diff --git a/src/IC/Canister/StableMemory.hs b/src/IC/Canister/StableMemory.hs
index 77d4fba8..33eee161 100644
--- a/src/IC/Canister/StableMemory.hs
+++ b/src/IC/Canister/StableMemory.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE StrictData #-}
 {-|
 This module provides a wrapper around primitive byte array, exposing just
 the bits needed for accessing the stable memory.
diff --git a/src/IC/Certificate.hs b/src/IC/Certificate.hs
index 760cfb8a..2d782351 100644
--- a/src/IC/Certificate.hs
+++ b/src/IC/Certificate.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE StrictData #-}
 module IC.Certificate where
 
 import IC.HashTree
diff --git a/src/IC/Crypto.hs b/src/IC/Crypto.hs
index bb2d011e..5199303c 100644
--- a/src/IC/Crypto.hs
+++ b/src/IC/Crypto.hs
@@ -3,6 +3,7 @@ Everything related to signature creation and checking
 -}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE StrictData #-}
 module IC.Crypto
  ( SecretKey(..)
  , createSecretKeyEd25519
diff --git a/src/IC/Crypto/BLS.hsc b/src/IC/Crypto/BLS.hsc
index b7fe10ce..623e1b5f 100644
--- a/src/IC/Crypto/BLS.hsc
+++ b/src/IC/Crypto/BLS.hsc
@@ -1,5 +1,6 @@
 {-# OPTIONS_GHC -fno-warn-unused-imports -Wno-unused-top-binds #-}
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE StrictData #-}
 #include <bls_BLS12381.h>
 module IC.Crypto.BLS
  ( init
diff --git a/src/IC/Crypto/Secp256k1.hs b/src/IC/Crypto/Secp256k1.hs
index 5e480f60..bbdfc79f 100644
--- a/src/IC/Crypto/Secp256k1.hs
+++ b/src/IC/Crypto/Secp256k1.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE BlockArguments #-}
+{-# LANGUAGE StrictData #-}
 module IC.Crypto.Secp256k1
  ( init
  , SecretKey
diff --git a/src/IC/Crypto/WebAuthn.hs b/src/IC/Crypto/WebAuthn.hs
index 0ca781e0..9b63e3ef 100644
--- a/src/IC/Crypto/WebAuthn.hs
+++ b/src/IC/Crypto/WebAuthn.hs
@@ -7,6 +7,7 @@ nesting of CBOR, DER and JSON…
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE BlockArguments #-}
+{-# LANGUAGE StrictData #-}
 module IC.Crypto.WebAuthn
  ( init
  , SecretKey
diff --git a/src/IC/DRun/Parse.hs b/src/IC/DRun/Parse.hs
index bf45207d..a663c896 100644
--- a/src/IC/DRun/Parse.hs
+++ b/src/IC/DRun/Parse.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE StrictData #-}
 module IC.DRun.Parse where
 
 import qualified Data.ByteString.Lazy.Char8 as B
diff --git a/src/IC/HTTP.hs b/src/IC/HTTP.hs
index c5892451..0cec6451 100644
--- a/src/IC/HTTP.hs
+++ b/src/IC/HTTP.hs
@@ -9,7 +9,7 @@ import Network.HTTP.Types
 import qualified Data.Text as T
 import qualified Data.Text.Encoding as T
 import Data.ByteString.Builder (stringUtf8)
-import Control.Monad.State
+import Control.Monad.State.Strict
 import Control.Monad.Except
 import Data.Aeson as JSON
 import Codec.Candid (Principal(..), parsePrincipal)
diff --git a/src/IC/HTTP/GenR.hs b/src/IC/HTTP/GenR.hs
index 15afb5ca..69a26f70 100644
--- a/src/IC/HTTP/GenR.hs
+++ b/src/IC/HTTP/GenR.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE StrictData #-}
 {-|
 This module describe a type for our “generic request (or response)” format. It
 can be seen as a simplified (and more abstract) AST for CBOR data.
diff --git a/src/IC/HTTP/GenR/Parse.hs b/src/IC/HTTP/GenR/Parse.hs
index f4a344a1..d1fffef4 100644
--- a/src/IC/HTTP/GenR/Parse.hs
+++ b/src/IC/HTTP/GenR/Parse.hs
@@ -12,7 +12,7 @@ module IC.HTTP.GenR.Parse where
 import Numeric.Natural
 import qualified Data.Text as T
 import qualified Data.ByteString.Lazy as BS
-import Control.Monad.State
+import Control.Monad.State.Strict
 import Control.Monad.Writer
 import Control.Monad.Except
 import qualified Data.HashMap.Lazy as HM
diff --git a/src/IC/Ref/Types.hs b/src/IC/Ref/Types.hs
index 10259fb0..31526a76 100644
--- a/src/IC/Ref/Types.hs
+++ b/src/IC/Ref/Types.hs
@@ -14,6 +14,7 @@
 {-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE NumericUnderscores #-}
 {-# LANGUAGE MultiWayIf #-}
+{-# LANGUAGE StrictData #-}
 
 {-|
 This module implements the main abstract types of the Internet Computer.
diff --git a/src/IC/StateFile.hs b/src/IC/StateFile.hs
index 94c26496..b9f6f09c 100644
--- a/src/IC/StateFile.hs
+++ b/src/IC/StateFile.hs
@@ -19,13 +19,14 @@ be safe to kill the process; _a_ recent state will be persisted.
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE BlockArguments #-}
+{-# LANGUAGE StrictData #-}
 module IC.StateFile (Store, withStore, modifyStore, peekStore) where
 
 import Codec.Serialise
 import qualified Data.ByteString.Lazy as BS
 import Control.Concurrent
 import Control.Exception
-import Control.Monad.State
+import Control.Monad.State.Strict
 import Data.IORef
 import System.AtomicWrite.Writer.LazyByteString.Binary
 import System.Directory
@@ -81,7 +82,7 @@ modifyStore :: Serialise a => Store a -> StateT a IO b -> IO b
 modifyStore store action =
     modifyMVar (stateVar store) $ \(!s) -> do
         n1 <- makeStableName s
-        (x, s') <- runStateT action s
+        (x, !s') <- runStateT action s
         n2 <- makeStableName s'
         -- If the stable names are the same, this means
         -- that the state is unchanged. No need to write new state
diff --git a/src/IC/Test/Agent.hs b/src/IC/Test/Agent.hs
index 2b1af6b3..e045f7ed 100644
--- a/src/IC/Test/Agent.hs
+++ b/src/IC/Test/Agent.hs
@@ -28,6 +28,7 @@ This module can also be used in a REPL; see 'connect'.
 {-# LANGUAGE NumericUnderscores #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE StrictData #-}
 module IC.Test.Agent
     (
       HTTPErrOr,
diff --git a/src/IC/Test/Spec.hs b/src/IC/Test/Spec.hs
index 941b6f79..24259c9a 100644
--- a/src/IC/Test/Spec.hs
+++ b/src/IC/Test/Spec.hs
@@ -11,6 +11,7 @@ This module contains a test suite for the Internet Computer
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE StrictData #-}
 
 module IC.Test.Spec (icTests) where
 
diff --git a/src/IC/Test/Spec/HTTP.hs b/src/IC/Test/Spec/HTTP.hs
index 2c1f04ba..11bb8373 100644
--- a/src/IC/Test/Spec/HTTP.hs
+++ b/src/IC/Test/Spec/HTTP.hs
@@ -11,6 +11,7 @@ This module contains a test suite for the Internet Computer
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE StrictData #-}
 
 module IC.Test.Spec.HTTP (canister_http_calls) where
 
diff --git a/src/IC/Test/Universal.hs b/src/IC/Test/Universal.hs
index 50c633b5..d9652c28 100644
--- a/src/IC/Test/Universal.hs
+++ b/src/IC/Test/Universal.hs
@@ -16,6 +16,7 @@ specification than this file and `universal-canister/src/`
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE StrictData #-}
 
 module IC.Test.Universal where
 
diff --git a/src/IC/Types.hs b/src/IC/Types.hs
index 97bbc34e..a4b6f88c 100644
--- a/src/IC/Types.hs
+++ b/src/IC/Types.hs
@@ -5,6 +5,7 @@
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE StrictData #-}
 module IC.Types where
 
 import qualified Data.ByteString.Lazy.Char8 as BS
diff --git a/src/IC/Utils.hs b/src/IC/Utils.hs
index 27dacf88..0417fc43 100644
--- a/src/IC/Utils.hs
+++ b/src/IC/Utils.hs
@@ -7,6 +7,7 @@
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE StrictData #-}
 {- |
 Generic utilities related to standard or imported data structures that we do
 don’t want to see in non-plumbing code.
diff --git a/src/IC/Wasm/Winter/Persist.hs b/src/IC/Wasm/Winter/Persist.hs
index 3021f9a2..116f4af3 100644
--- a/src/IC/Wasm/Winter/Persist.hs
+++ b/src/IC/Wasm/Winter/Persist.hs
@@ -3,6 +3,7 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE StrictData #-}
 {- |
 This module provides a way to persist the state of a Winter Wasm instance, and
 to recover it.