diff --git a/core/blockchain_ext_test.go b/core/blockchain_ext_test.go
index 566f85274a..1b4099f5ea 100644
--- a/core/blockchain_ext_test.go
+++ b/core/blockchain_ext_test.go
@@ -6,6 +6,8 @@ package core
 import (
 	"fmt"
 	"math/big"
+	"os"
+	"path/filepath"
 	"slices"
 	"testing"
 
@@ -164,6 +166,30 @@ func copyMemDB(db ethdb.Database) (ethdb.Database, error) {
 	return newDB, nil
 }
 
+// This copies all files from a flat directory [src] to a new temporary directory and returns
+// the path to the new directory.
+func copyFlatDir(t *testing.T, src string) string {
+	t.Helper()
+	if src == "" {
+		return ""
+	}
+
+	dst := t.TempDir()
+	ents, err := os.ReadDir(src)
+	require.NoError(t, err)
+
+	for _, e := range ents {
+		require.False(t, e.IsDir(), "expected flat directory")
+		name := e.Name()
+		data, err := os.ReadFile(filepath.Join(src, name))
+		require.NoError(t, err)
+		info, err := e.Info()
+		require.NoError(t, err)
+		require.NoError(t, os.WriteFile(filepath.Join(dst, name), data, info.Mode().Perm()))
+	}
+	return dst
+}
+
 // checkBlockChainState creates a new BlockChain instance and checks that exporting each block from
 // genesis to last accepted from the original instance yields the same last accepted block and state
 // root.
@@ -211,7 +237,8 @@ func checkBlockChainState(
 	// Copy the database over to prevent any issues when re-using [originalDB] after this call.
 	originalDB, err = copyMemDB(originalDB)
 	require.NoError(err)
-	restartedChain, err := create(originalDB, gspec, lastAcceptedBlock.Hash(), oldChainDataDir)
+	newChainDataDir := copyFlatDir(t, oldChainDataDir)
+	restartedChain, err := create(originalDB, gspec, lastAcceptedBlock.Hash(), newChainDataDir)
 	require.NoError(err)
 	defer restartedChain.Stop()
 	currentBlock := restartedChain.CurrentBlock()
diff --git a/go.mod b/go.mod
index 8ca8713da1..9fb08caed6 100644
--- a/go.mod
+++ b/go.mod
@@ -17,7 +17,7 @@ go 1.24.8
 require (
 	github.com/VictoriaMetrics/fastcache v1.12.1
 	github.com/ava-labs/avalanchego v1.13.6-0.20251007213349-63cc1a166a56
-	github.com/ava-labs/firewood-go-ethhash/ffi v0.0.12
+	github.com/ava-labs/firewood-go-ethhash/ffi v0.0.13
 	github.com/ava-labs/libevm v1.13.15-0.20251002164226-35926db4d661
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc
 	github.com/deckarep/golang-set/v2 v2.1.0
diff --git a/go.sum b/go.sum
index 50744d2ab5..eb74837482 100644
--- a/go.sum
+++ b/go.sum
@@ -28,8 +28,8 @@ github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5 h1:0CwZNZbxp69SHPd
 github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5/go.mod h1:wHh0iHkYZB8zMSxRWpUBQtwG5a7fFgvEO+odwuTv2gs=
 github.com/ava-labs/avalanchego v1.13.6-0.20251007213349-63cc1a166a56 h1:Q4lnXtjMwsIheyRUkuOU7EZZ9WFf28vMWG4lPCmqhaE=
 github.com/ava-labs/avalanchego v1.13.6-0.20251007213349-63cc1a166a56/go.mod h1:EL0MGbL2liE9jp4QtCHR2thkNl8hCkD26DJ+7cmcaqs=
-github.com/ava-labs/firewood-go-ethhash/ffi v0.0.12 h1:aMcrLbpJ/dyu2kZDf/Di/4JIWsUcYPyTDKymiHpejt0=
-github.com/ava-labs/firewood-go-ethhash/ffi v0.0.12/go.mod h1:cq89ua3iiZ5wPBALTEQS5eG8DIZcs7ov6OiL4YR1BVY=
+github.com/ava-labs/firewood-go-ethhash/ffi v0.0.13 h1:obPwnVCkF5+B2f8WbTepHj0ZgiW21vKUgFCtATuAYNY=
+github.com/ava-labs/firewood-go-ethhash/ffi v0.0.13/go.mod h1:gsGr1ICjokI9CyPaaRHMqDoDCaT1VguC/IyOTx6rJ14=
 github.com/ava-labs/libevm v1.13.15-0.20251002164226-35926db4d661 h1:lt4yQE1HMvxWrdD5RFj+h9kWUsZK2rmNohvkeQsbG9M=
 github.com/ava-labs/libevm v1.13.15-0.20251002164226-35926db4d661/go.mod h1:ivRC/KojP8sai7j8WnpXIReQpcRklL2bIzoysnjpARQ=
 github.com/aymerick/raymond v2.0.3-0.20180322193309-b565731e1464+incompatible/go.mod h1:osfaiScAUVup+UC9Nfq76eWqDhXlp+4UYaA8uhTBO6g=