diff --git a/package-lock.json b/package-lock.json
index 4400c1f..b72d9f9 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9,7 +9,9 @@
       "version": "0.1.0",
       "license": "Apache-2.0",
       "dependencies": {
+        "@types/rfdc": "^1.2.0",
         "@types/semver": "^7.5.8",
+        "rfdc": "^1.3.1",
         "semver": "^7.6.0"
       },
       "devDependencies": {
@@ -169,6 +171,15 @@
         "undici-types": "~5.26.4"
       }
     },
+    "node_modules/@types/rfdc": {
+      "version": "1.2.0",
+      "resolved": "https://registry.npmjs.org/@types/rfdc/-/rfdc-1.2.0.tgz",
+      "integrity": "sha512-9Q81yCQwj4iuqDWVEcZMaY3QJ+w+Vj3M71ZdobgFC6T+RowLlE5CaLwRrwMiFvE3LZ7Qy1SDrR+EjGtVu9FmJQ==",
+      "deprecated": "This is a stub types definition. rfdc provides its own type definitions, so you do not need this installed.",
+      "dependencies": {
+        "rfdc": "*"
+      }
+    },
     "node_modules/@types/semver": {
       "version": "7.5.8",
       "resolved": "https://registry.npmjs.org/@types/semver/-/semver-7.5.8.tgz",
@@ -882,6 +893,11 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/rfdc": {
+      "version": "1.3.1",
+      "resolved": "https://registry.npmjs.org/rfdc/-/rfdc-1.3.1.tgz",
+      "integrity": "sha512-r5a3l5HzYlIC68TpmYKlxWjmOP6wiPJ1vWv2HeLhNsRZMrCkxeqxiHlQ21oXmQ4F3SiryXBHhAD7JZqvOJjFmg=="
+    },
     "node_modules/semver": {
       "version": "7.6.0",
       "resolved": "https://registry.npmjs.org/semver/-/semver-7.6.0.tgz",
diff --git a/package.json b/package.json
index 5f42f37..2ef085e 100644
--- a/package.json
+++ b/package.json
@@ -37,6 +37,8 @@
     "borp": "^0.10.0",
     "desm": "^1.3.1",
     "prettier": "^3.2.5",
+    "@types/rfdc": "^1.2.0",
+    "@types/semver": "^7.5.8",
     "typescript": "^5.3.3"
   },
   "prettier": {
@@ -57,7 +59,7 @@
   "main": "./dist/semgrator.js",
   "types": "./dist/semgrator.d.ts",
   "dependencies": {
-    "@types/semver": "^7.5.8",
+    "rfdc": "^1.3.1",
     "semver": "^7.6.0"
   }
 }
diff --git a/src/lib/semgrator.ts b/src/lib/semgrator.ts
index 85383e9..c4b6ae3 100644
--- a/src/lib/semgrator.ts
+++ b/src/lib/semgrator.ts
@@ -2,6 +2,9 @@ import semver from 'semver'
 import { join } from 'node:path'
 import { pathToFileURL } from 'node:url'
 import { readdir } from 'node:fs/promises'
+import rfdc from 'rfdc'
+
+const clone = rfdc()
 
 export type Migration<Input, Output = Input> = {
   version: string
@@ -87,7 +90,7 @@ async function* processMigrations<Input, Output>(
   for await (const migration of migrations) {
     if (semver.gt(migration.version, lastVersion)) {
       // @ts-expect-error
-      result = await migration.up(result)
+      result = await migration.up(clone(result))
       lastVersion = migration.toVersion || migration.version
       changed = true
     }
diff --git a/src/test/semgrator.test.ts b/src/test/semgrator.test.ts
index 11a1ee5..5c300ef 100644
--- a/src/test/semgrator.test.ts
+++ b/src/test/semgrator.test.ts
@@ -2,13 +2,17 @@ import { test } from 'node:test'
 import { semgrator, Migration } from '../lib/semgrator.js'
 import { tspl } from '@matteo.collina/tspl'
 import { throws } from 'node:assert/strict'
+import { equal, deepEqual } from 'node:assert/strict'
 
 type SeenBy = {
   foo: string
   seenBy?: string
+  deep?: {
+    seenBy?: string
+  }
 }
 
-test('apply all  migrations', async t => {
+test('apply all migrations', async t => {
   const plan = tspl(t, { plan: 4 })
   const m1: Migration<SeenBy> = {
     version: '2.0.0',
@@ -207,3 +211,44 @@ test('throws if version is missing', async t => {
     },
   )
 })
+
+test('clones at each step', async t => {
+  const m1: Migration<SeenBy> = {
+    version: '2.0.0',
+    async up(input) {
+      input.seenBy = '2.0.0'
+      input.deep ||= {}
+      input.deep.seenBy = '2.0.0'
+      return input
+    },
+  }
+
+  const input = {
+    foo: 'bar',
+    deep: {
+      seenBy: '1.0.0',
+    },
+  }
+
+  const res = await semgrator<SeenBy, SeenBy>({
+    version: '1.0.0',
+    migrations: [m1],
+    input,
+  })
+
+  equal(res.version, '2.0.0')
+  equal(res.changed, true)
+  deepEqual(res.result, {
+    foo: 'bar',
+    seenBy: '2.0.0',
+    deep: {
+      seenBy: '2.0.0',
+    },
+  })
+  deepEqual(input, {
+    foo: 'bar',
+    deep: {
+      seenBy: '1.0.0',
+    },
+  })
+})