diff --git a/src/app/api/affiliates/offers/[id]/route.test.ts b/src/app/api/affiliates/offers/[id]/route.test.ts
index ecc76a6a..1be6f75e 100644
--- a/src/app/api/affiliates/offers/[id]/route.test.ts
+++ b/src/app/api/affiliates/offers/[id]/route.test.ts
@@ -19,12 +19,20 @@ vi.mock("@/lib/affiliates/validation", () => ({
   validateOfferInput: vi.fn(),
 }));
 
-import { GET } from "./route";
+import { GET, PATCH } from "./route";
 
 function makeRequest(id: string) {
   return new NextRequest(`http://localhost/api/affiliates/offers/${id}`);
 }
 
+function makePatchRequest(id: string, body: Record<string, unknown>) {
+  return new NextRequest(`http://localhost/api/affiliates/offers/${id}`, {
+    method: "PATCH",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
 function makeParams(id: string) {
   return { params: Promise.resolve({ id }) };
 }
@@ -113,3 +121,36 @@ describe("GET /api/affiliates/offers/[id]", () => {
     expect(res.status).toBe(404);
   });
 });
+
+describe("PATCH /api/affiliates/offers/[id]", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockGetAuthContext.mockResolvedValue({ user: { id: "seller1" } });
+  });
+
+  it("rejects non-string title updates", async () => {
+    mockFrom.mockReturnValue(chainable({ id: "offer1", seller_id: "seller1" }));
+
+    const res = await PATCH(
+      makePatchRequest("offer1", { title: 123 }),
+      makeParams("offer1")
+    );
+    const body = await res.json();
+
+    expect(res.status).toBe(400);
+    expect(body.error).toBe("title must be a string");
+  });
+
+  it("rejects non-string description updates", async () => {
+    mockFrom.mockReturnValue(chainable({ id: "offer1", seller_id: "seller1" }));
+
+    const res = await PATCH(
+      makePatchRequest("offer1", { description: { text: "not a string" } }),
+      makeParams("offer1")
+    );
+    const body = await res.json();
+
+    expect(res.status).toBe(400);
+    expect(body.error).toBe("description must be a string");
+  });
+});
diff --git a/src/app/api/affiliates/offers/[id]/route.ts b/src/app/api/affiliates/offers/[id]/route.ts
index eec125d1..b00954b8 100644
--- a/src/app/api/affiliates/offers/[id]/route.ts
+++ b/src/app/api/affiliates/offers/[id]/route.ts
@@ -2,7 +2,6 @@ import { NextRequest, NextResponse } from "next/server";
 import { getAuthContext } from "@/lib/auth/get-user";
 import { createServiceClient } from "@/lib/supabase/service";
 
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
 type AnySupabase = any;
 import { validateOfferInput } from "@/lib/affiliates/validation";
 
@@ -100,8 +99,18 @@ export async function PATCH(
     // Partial validation — only validate provided fields
     const updateData: Record<string, unknown> = { updated_at: new Date().toISOString() };
 
-    if (body.title !== undefined) updateData.title = body.title.trim();
-    if (body.description !== undefined) updateData.description = body.description.trim();
+    if (body.title !== undefined) {
+      if (typeof body.title !== "string") {
+        return NextResponse.json({ error: "title must be a string" }, { status: 400 });
+      }
+      updateData.title = body.title.trim();
+    }
+    if (body.description !== undefined) {
+      if (typeof body.description !== "string") {
+        return NextResponse.json({ error: "description must be a string" }, { status: 400 });
+      }
+      updateData.description = body.description.trim();
+    }
     if (body.product_url !== undefined) updateData.product_url = body.product_url;
     if (body.product_type !== undefined) updateData.product_type = body.product_type;
     if (body.price_sats !== undefined) updateData.price_sats = body.price_sats;