diff --git a/src/sandbox/sandbox-config.ts b/src/sandbox/sandbox-config.ts
index baa6052d..df21ba6a 100644
--- a/src/sandbox/sandbox-config.ts
+++ b/src/sandbox/sandbox-config.ts
@@ -1140,6 +1140,10 @@ export const SandboxRuntimeConfigSchema = z
         '`safe.directory` without adding them to `filesystem.allowWrite`.',
     ),
   })
+  // Reject unknown top-level keys so a typo like `denyWriteTypo` fails
+  // loudly instead of being silently stripped while the operator believes
+  // the policy is enforced. Same reasoning as the strict sub-schemas above.
+  .strict()
   .superRefine((cfg, ctx) => {
     const creds = cfg.credentials
     if (!creds) return
diff --git a/test/config-validation.test.ts b/test/config-validation.test.ts
index a041958b..c6ec63db 100644
--- a/test/config-validation.test.ts
+++ b/test/config-validation.test.ts
@@ -2,20 +2,20 @@ import { describe, test, expect } from 'bun:test'
 import { SandboxRuntimeConfigSchema } from '../src/sandbox/sandbox-config.js'
 
 describe('Config Validation', () => {
-  test('should validate a valid minimal config', () => {
-    const config = {
-      network: {
-        allowedDomains: [],
-        deniedDomains: [],
-      },
-      filesystem: {
-        denyRead: [],
-        allowWrite: [],
-        denyWrite: [],
-      },
-    }
+  const validConfig = {
+    network: {
+      allowedDomains: [],
+      deniedDomains: [],
+    },
+    filesystem: {
+      denyRead: [],
+      allowWrite: [],
+      denyWrite: [],
+    },
+  }
 
-    const result = SandboxRuntimeConfigSchema.safeParse(config)
+  test('should validate a valid minimal config', () => {
+    const result = SandboxRuntimeConfigSchema.safeParse(validConfig)
     expect(result.success).toBe(true)
   })
 
@@ -127,6 +127,35 @@ describe('Config Validation', () => {
     expect(result.success).toBe(false)
   })
 
+  test('should reject unknown top-level keys', () => {
+    // A typo like `denyWriteTypo` must fail loudly instead of being
+    // silently stripped while the operator believes the policy is
+    // enforced (issue #434).
+    const config = {
+      ...validConfig,
+      denyWriteTypo: ['/Users/me'],
+    }
+
+    const result = SandboxRuntimeConfigSchema.safeParse(config)
+    expect(result.success).toBe(false)
+    if (!result.success) {
+      const messages = result.error.issues.map(issue => issue.message)
+      expect(messages.some(message => message.includes('denyWriteTypo'))).toBe(
+        true,
+      )
+    }
+  })
+
+  test('should still reject unknown top-level keys alongside valid config', () => {
+    const config = {
+      ...validConfig,
+      allowEverything: true,
+    }
+
+    const result = SandboxRuntimeConfigSchema.safeParse(config)
+    expect(result.success).toBe(false)
+  })
+
   test('should validate wildcard domains correctly', () => {
     const validWildcards = ['*.example.com', '*.github.io', '*.co.uk']