diff --git a/services/platform-service/src/modules/support-cases/routes.test.ts b/services/platform-service/src/modules/support-cases/routes.test.ts
index ddba2d94..f3ccc5c3 100644
--- a/services/platform-service/src/modules/support-cases/routes.test.ts
+++ b/services/platform-service/src/modules/support-cases/routes.test.ts
@@ -225,6 +225,30 @@ describe('supportCaseRoutes', () => {
     expect(body.tagsAdded).toContain('category:billing');
   });
 
+  it('POST /support/cases/:id/auto-triage handles undefined tags gracefully', async () => {
+    repoMock.getCase.mockResolvedValue({
+      id: 'sup_3',
+      productId: 'lysnrai',
+      title: 'Slow dashboard loading',
+      description: 'Pages take 10s to load',
+      priority: 'low',
+      // tags intentionally omitted — undefined
+    });
+    repoMock.updateCase.mockImplementation(
+      async (_id: string, _pid: string, updates: Record<string, unknown>) => ({
+        ...updates,
+        id: 'sup_3',
+      })
+    );
+    const app = await buildApp({ sub: 'admin_1', productId: 'lysnrai', role: 'admin' });
+
+    const res = await app.inject({ method: 'POST', url: '/api/support/cases/sup_3/auto-triage' });
+    expect(res.statusCode).toBe(200);
+    const body = res.json();
+    expect(body.newPriority).toBe('medium');
+    expect(body.tagsAdded).toContain('auto-triaged:medium');
+  });
+
   // ── Case Metrics ───────────────────────────────────────
 
   it('GET /support/metrics returns case metrics with SLA compliance', async () => {
diff --git a/services/platform-service/src/modules/support-cases/routes.ts b/services/platform-service/src/modules/support-cases/routes.ts
index 4aae81f0..a7f9e647 100644
--- a/services/platform-service/src/modules/support-cases/routes.ts
+++ b/services/platform-service/src/modules/support-cases/routes.ts
@@ -254,7 +254,7 @@ export async function supportCaseRoutes(app: FastifyInstance) {
     const text = `${supportCase.title} ${supportCase.description ?? ''}`.toLowerCase();
 
     let suggestedPriority: string = supportCase.priority;
-    const tags = [...supportCase.tags];
+    const tags = [...(supportCase.tags ?? [])];
 
     // Priority heuristics
     if (text.includes('outage') || text.includes('production down') || text.includes('data loss')) {
@@ -293,7 +293,7 @@ export async function supportCaseRoutes(app: FastifyInstance) {
       triaged: true,
       previousPriority: supportCase.priority,
       newPriority: suggestedPriority,
-      tagsAdded: dedupedTags.filter(t => !supportCase.tags.includes(t)),
+      tagsAdded: dedupedTags.filter(t => !(supportCase.tags ?? []).includes(t)),
       case: updated,
     };
   });