diff --git a/src/data/dto/chat/__tests__/unlock_private_response.test.ts b/src/data/dto/chat/__tests__/unlock_private_response.test.ts
index d16ac68d..b9ad2fa7 100644
--- a/src/data/dto/chat/__tests__/unlock_private_response.test.ts
+++ b/src/data/dto/chat/__tests__/unlock_private_response.test.ts
@@ -79,4 +79,29 @@ describe("UnlockPrivateResponse", () => {
 
     expect(response.content).toBe("");
   });
+
+  it("defaults nullable credit fields to zero", () => {
+    const response = UnlockPrivateResponse.from({
+      unlocked: false,
+      content: "",
+      reason: "insufficient_balance",
+      creditBalance: null,
+      creditsCharged: null,
+      requiredCredits: null,
+      shortfallCredits: null,
+      lockDetail: {
+        locked: true,
+        showContent: false,
+        showUpgrade: true,
+        reason: "insufficient_balance",
+        hint: null,
+        detail: null,
+      },
+    });
+
+    expect(response.creditBalance).toBe(0);
+    expect(response.creditsCharged).toBe(0);
+    expect(response.requiredCredits).toBe(0);
+    expect(response.shortfallCredits).toBe(0);
+  });
 });
diff --git a/src/data/schemas/chat/unlock_private_response.ts b/src/data/schemas/chat/unlock_private_response.ts
index d7c30210..08f74ab3 100644
--- a/src/data/schemas/chat/unlock_private_response.ts
+++ b/src/data/schemas/chat/unlock_private_response.ts
@@ -1,6 +1,6 @@
 import { z } from "zod";
 
-import { stringOrEmpty } from "../nullable-defaults";
+import { numberOrZero, stringOrEmpty } from "../nullable-defaults";
 import { ChatLockDetailSchema } from "./chat_payloads";
 
 /**
@@ -12,10 +12,10 @@ export const UnlockPrivateResponseSchema = z.object({
   unlocked: z.boolean(),
   content: stringOrEmpty,
   reason: UnlockPrivateReasonSchema,
-  creditBalance: z.number().default(0),
-  creditsCharged: z.number().default(0),
-  requiredCredits: z.number().default(0),
-  shortfallCredits: z.number().default(0),
+  creditBalance: numberOrZero,
+  creditsCharged: numberOrZero,
+  requiredCredits: numberOrZero,
+  shortfallCredits: numberOrZero,
   lockDetail: ChatLockDetailSchema,
 });