diff --git a/core/blockchain_ext_test.go b/core/blockchain_ext_test.go
index 717efc0071..1b5d32ede7 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"
 
@@ -139,6 +141,30 @@ 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.
@@ -205,7 +231,8 @@ func checkBlockChainState(
 	if err != nil {
 		t.Fatal(err)
 	}
-	restartedChain, err := create(originalDB, gspec, lastAcceptedBlock.Hash(), oldChainDataDir)
+	newChainDataDir := copyFlatDir(t, oldChainDataDir)
+	restartedChain, err := create(originalDB, gspec, lastAcceptedBlock.Hash(), newChainDataDir)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/go.mod b/go.mod
index 3cb59c3147..ae2f44944c 100644
--- a/go.mod
+++ b/go.mod
@@ -6,7 +6,7 @@ require (
 	github.com/VictoriaMetrics/fastcache v1.12.1
 	github.com/antithesishq/antithesis-sdk-go v0.3.8
 	github.com/ava-labs/avalanchego v1.13.6-rc.1
-	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 40260a3058..168fdcc467 100644
--- a/go.sum
+++ b/go.sum
@@ -32,8 +32,8 @@ github.com/ava-labs/avalanchego v1.13.6-rc.1 h1:O4qeGhxRVO5O8vfu2LMpwU5AdES/8bB2
 github.com/ava-labs/avalanchego v1.13.6-rc.1/go.mod h1:27SGpJ0L+3jVMfjY8X5nmgkZ3sFSc7vGeJj+SFjAKL0=
 github.com/ava-labs/coreth v0.15.4-rc.4 h1:ze7/IwDptWG1u2d32uUZz9Ix9ycVUtlB8JufuSKSSS4=
 github.com/ava-labs/coreth v0.15.4-rc.4/go.mod h1:yVwuMyPkZ48xzZ0y2OdIwaoUqvSsgPYoodyX9BZJ2uo=
-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=