diff --git a/migrate/chaindb4to5.js b/migrate/chaindb4to5.js
new file mode 100644
index 00000000..585fc868
--- /dev/null
+++ b/migrate/chaindb4to5.js
@@ -0,0 +1,115 @@
+'use strict';
+
+const assert = require('assert');
+const bdb = require('bdb');
+const layout = require('../lib/blockchain/layout');
+const FileBlockStore = require('../lib/blockstore/file');
+const fs = require('bfile');
+const {resolve} = require('path');
+
+assert(process.argv.length > 2, 'Please pass in a database path.');
+
+// migration -
+// chaindb: leveldb to flat files
+
+const db = bdb.create({
+  location: process.argv[2],
+  memory: false,
+  compression: true,
+  cacheSize: 32 << 20,
+  createIfMissing: false
+});
+
+async function ensure(location) {
+  if (fs.unsupported)
+    return undefined;
+
+  return fs.mkdirp(location);
+}
+
+const location = resolve(process.argv[2], '../blocks');
+
+const blockStore = new FileBlockStore({
+  location: location
+});
+
+async function updateVersion() {
+  const ver = await checkVersion();
+
+  console.log('Updating version to %d.', ver + 1);
+
+  const buf = Buffer.allocUnsafe(5 + 4);
+  buf.write('chain', 0, 'ascii');
+  buf.writeUInt32LE(5, 5, true);
+
+  const parent = db.batch();
+  parent.put(layout.V.encode(), buf);
+  await parent.write();
+}
+
+async function checkVersion() {
+  console.log('Checking version.');
+
+  const data = await db.get(layout.V.encode());
+  assert(data, 'No version.');
+
+  const ver = data.readUInt32LE(5, true);
+
+  if (ver !== 4)
+    throw Error(`DB is version ${ver}.`);
+
+  return ver;
+}
+
+async function migrateBlocks() {
+  console.log('Migrating blocks');
+
+  let parent = db.batch();
+
+  const iter = db.iterator({
+    gte: layout.b.min(),
+    lte: layout.b.max(),
+    keys: true,
+    values: true
+  });
+
+  let total = 0;
+  await iter.each(async (key, value) => {
+    const hash = key.slice(1);
+    await blockStore.write(hash, value);
+    parent.del(key);
+
+    if (++total % 10000 === 0) {
+      console.log('Migrated up %d blocks.', total);
+      await parent.write();
+      parent = db.batch();
+    }
+  });
+  await parent.write();
+}
+
+/*
+ * Execute
+ */
+
+(async () => {
+  await db.open();
+  await ensure(location);
+  await blockStore.open();
+
+  console.log('Opened %s.', process.argv[2]);
+
+  await checkVersion();
+  await migrateBlocks();
+  await updateVersion();
+
+  await db.compactRange();
+  await db.close();
+  await blockStore.close();
+})().then(() => {
+  console.log('Migration complete.');
+  process.exit(0);
+}).catch((err) => {
+  console.error(err.stack);
+  process.exit(1);
+});