diff --git a/apps/web/src/lib/server/integrations/segment/__tests__/user-sync.test.ts b/apps/web/src/lib/server/integrations/segment/__tests__/user-sync.test.ts
index 52de899e7..0bde1aee2 100644
--- a/apps/web/src/lib/server/integrations/segment/__tests__/user-sync.test.ts
+++ b/apps/web/src/lib/server/integrations/segment/__tests__/user-sync.test.ts
@@ -1,6 +1,63 @@
+import { createHmac } from 'crypto'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { segmentUserSync } from '../user-sync'
 
+describe('segmentUserSync.handleIdentify', () => {
+  const body = JSON.stringify({
+    type: 'identify',
+    userId: 'external-user-1',
+    traits: { email: 'user@example.com', plan: 'pro' },
+  })
+
+  it('rejects unsigned identify requests when no incoming secret is configured', async () => {
+    const request = new Request('https://example.com/api/integrations/segment/identify', {
+      method: 'POST',
+    })
+
+    const result = await segmentUserSync.handleIdentify?.(request, body, {}, {})
+
+    expect(result).toBeInstanceOf(Response)
+    expect((result as Response).status).toBe(401)
+    await expect((result as Response).text()).resolves.toBe(
+      'Segment incoming secret is not configured'
+    )
+  })
+
+  it('rejects identify requests when an incoming secret is configured but the signature is missing', async () => {
+    const request = new Request('https://example.com/api/integrations/segment/identify', {
+      method: 'POST',
+    })
+
+    const result = await segmentUserSync.handleIdentify?.(
+      request,
+      body,
+      { incomingSecret: 'segment-secret' },
+      {}
+    )
+
+    expect(result).toBeInstanceOf(Response)
+    expect((result as Response).status).toBe(401)
+    await expect((result as Response).text()).resolves.toBe('Missing x-signature header')
+  })
+
+  it('accepts identify requests with a valid signature', async () => {
+    const incomingSecret = 'segment-secret'
+    const signature = createHmac('sha1', incomingSecret).update(body).digest('base64')
+    const request = new Request('https://example.com/api/integrations/segment/identify', {
+      method: 'POST',
+      headers: { 'x-signature': signature },
+    })
+
+    const result = await segmentUserSync.handleIdentify?.(request, body, { incomingSecret }, {})
+
+    expect(result).toEqual({
+      email: 'user@example.com',
+      externalUserId: 'external-user-1',
+      attributes: { email: 'user@example.com', plan: 'pro' },
+    })
+  })
+})
+
 describe('segmentUserSync.syncSegmentMembership', () => {
   beforeEach(() => {
     vi.restoreAllMocks()
diff --git a/apps/web/src/lib/server/integrations/segment/user-sync.ts b/apps/web/src/lib/server/integrations/segment/user-sync.ts
index f1a4dba3d..d1658cfaf 100644
--- a/apps/web/src/lib/server/integrations/segment/user-sync.ts
+++ b/apps/web/src/lib/server/integrations/segment/user-sync.ts
@@ -27,25 +27,27 @@ const MAX_ERROR_BODY_LENGTH = 300
 
 export const segmentUserSync: UserSyncHandler = {
   async handleIdentify(request, body, config, _secrets): Promise<UserIdentifyPayload | Response> {
-    // Verify HMAC-SHA1 signature if a shared secret is configured.
-    // Segment signs the raw body with the source's shared secret.
-    const incomingSecret = config.incomingSecret as string | undefined
-    if (incomingSecret) {
-      const signature = request.headers.get('x-signature')
-      if (!signature) {
-        return new Response('Missing x-signature header', { status: 401 })
-      }
+    // Segment identify webhooks mutate user metadata, so require a shared secret
+    // and verify every inbound request before parsing the payload.
+    const incomingSecret = config.incomingSecret
+    if (typeof incomingSecret !== 'string' || incomingSecret.trim().length === 0) {
+      return new Response('Segment incoming secret is not configured', { status: 401 })
+    }
 
-      const expected = createHmac('sha1', incomingSecret).update(body).digest('base64')
-      try {
-        const sigBuf = Buffer.from(signature, 'base64')
-        const expBuf = Buffer.from(expected, 'base64')
-        if (sigBuf.length !== expBuf.length || !timingSafeEqual(sigBuf, expBuf)) {
-          return new Response('Invalid signature', { status: 401 })
-        }
-      } catch {
+    const signature = request.headers.get('x-signature')
+    if (!signature) {
+      return new Response('Missing x-signature header', { status: 401 })
+    }
+
+    const expected = createHmac('sha1', incomingSecret).update(body).digest('base64')
+    try {
+      const sigBuf = Buffer.from(signature, 'base64')
+      const expBuf = Buffer.from(expected, 'base64')
+      if (sigBuf.length !== expBuf.length || !timingSafeEqual(sigBuf, expBuf)) {
         return new Response('Invalid signature', { status: 401 })
       }
+    } catch {
+      return new Response('Invalid signature', { status: 401 })
     }
 
     let payload: Record<string, unknown>