diff --git a/.changeset/chilly-glasses-fetch.md b/.changeset/chilly-glasses-fetch.md
new file mode 100644
index 0000000000..7e1b85c8f7
--- /dev/null
+++ b/.changeset/chilly-glasses-fetch.md
@@ -0,0 +1,5 @@
+---
+'@shopify/app': patch
+---
+
+Fix crash "config2.map is not a function" in `rewriteConfiguration` when writing app configuration with unvalidated data (e.g., from third-party templates without `client_id`)
diff --git a/packages/app/src/cli/services/app/write-app-configuration-file.test.ts b/packages/app/src/cli/services/app/write-app-configuration-file.test.ts
index 685e53f959..44f129c073 100644
--- a/packages/app/src/cli/services/app/write-app-configuration-file.test.ts
+++ b/packages/app/src/cli/services/app/write-app-configuration-file.test.ts
@@ -1,8 +1,9 @@
-import {writeAppConfigurationFile} from './write-app-configuration-file.js'
+import {rewriteConfiguration, writeAppConfigurationFile} from './write-app-configuration-file.js'
 import {DEFAULT_CONFIG, buildVersionedAppSchema} from '../../models/app/app.test-data.js'
 import {CurrentAppConfiguration} from '../../models/app/app.js'
 import {inTemporaryDirectory, readFile} from '@shopify/cli-kit/node/fs'
 import {joinPath} from '@shopify/cli-kit/node/path'
+import {zod} from '@shopify/cli-kit/node/schema'
 import {describe, expect, test} from 'vitest'
 
 const FULL_CONFIGURATION = {
@@ -151,3 +152,59 @@ url = "https://example.com/prefs"
     })
   })
 })
+
+describe('rewriteConfiguration', () => {
+  test('handles undefined config for an optional array schema wrapped in effects', () => {
+    const schema = zod.array(zod.string()).optional().transform((val) => val)
+
+    expect(rewriteConfiguration(schema, undefined)).toBeUndefined()
+  })
+
+  test('handles null config for an array schema', () => {
+    const schema = zod.array(zod.string())
+
+    expect(rewriteConfiguration(schema, null)).toBeNull()
+  })
+
+  test('handles undefined config for an object schema', () => {
+    const schema = zod.object({name: zod.string()}).optional()
+
+    expect(rewriteConfiguration(schema, undefined)).toBeUndefined()
+  })
+
+  test('handles null config for a nullable object schema', () => {
+    const schema = zod.object({name: zod.string()}).nullable()
+
+    expect(rewriteConfiguration(schema, null)).toBeNull()
+  })
+
+  test('passes through non-array value when schema expects an array', () => {
+    const schema = zod.array(zod.string())
+
+    expect(rewriteConfiguration(schema, 'not-an-array')).toBe('not-an-array')
+  })
+
+  test('passes through non-object value when schema expects an object', () => {
+    const schema = zod.object({name: zod.string()})
+
+    expect(rewriteConfiguration(schema, 'not-an-object')).toBe('not-an-object')
+  })
+
+  test('passes through array value when schema expects an object', () => {
+    const schema = zod.object({name: zod.string()})
+
+    const input = ['a', 'b']
+    expect(rewriteConfiguration(schema, input)).toBe(input)
+  })
+
+  test('does not crash with type-mismatched config against the real app schema', async () => {
+    const {schema} = await buildVersionedAppSchema()
+    const malformedConfig = {
+      ...DEFAULT_CONFIG,
+      auth: {redirect_urls: 'not-an-array'},
+      webhooks: {api_version: '2023-07', subscriptions: 'also-not-an-array'},
+    }
+
+    expect(() => rewriteConfiguration(schema, malformedConfig)).not.toThrow()
+  })
+})
diff --git a/packages/app/src/cli/services/app/write-app-configuration-file.ts b/packages/app/src/cli/services/app/write-app-configuration-file.ts
index c2f8201240..7dbcc53236 100644
--- a/packages/app/src/cli/services/app/write-app-configuration-file.ts
+++ b/packages/app/src/cli/services/app/write-app-configuration-file.ts
@@ -27,15 +27,18 @@ export async function writeAppConfigurationFile(
 
 export const rewriteConfiguration = <T extends zod.ZodTypeAny>(schema: T, config: unknown): unknown => {
   if (schema === null || schema === undefined) return null
+  if (config === null || config === undefined) return config
   if (schema instanceof zod.ZodNullable || schema instanceof zod.ZodOptional)
     return rewriteConfiguration(schema.unwrap(), config)
   if (schema instanceof zod.ZodArray) {
-    return (config as unknown[]).map((item) => rewriteConfiguration(schema.element, item))
+    if (!Array.isArray(config)) return config
+    return config.map((item) => rewriteConfiguration(schema.element, item))
   }
   if (schema instanceof zod.ZodEffects) {
     return rewriteConfiguration(schema._def.schema, config)
   }
   if (schema instanceof zod.ZodObject) {
+    if (typeof config !== 'object' || Array.isArray(config)) return config
     const entries = Object.entries(schema.shape)
     const confObj = config as {[key: string]: unknown}
     let result: {[key: string]: unknown} = {}