diff --git a/src/__tests__/whoop/client.test.ts b/src/__tests__/whoop/client.test.ts
index 3557135..7a22490 100644
--- a/src/__tests__/whoop/client.test.ts
+++ b/src/__tests__/whoop/client.test.ts
@@ -232,6 +232,19 @@ describe("WHOOP v2 client", () => {
     );
   });
 
+  it("treats a live null next token as collection exhaustion", async () => {
+    vi.spyOn(globalThis, "fetch").mockResolvedValue(jsonResponse({
+      records: [SLEEP],
+      next_token: null,
+    }));
+    const client = new WhoopClient(ENV, "access");
+
+    await expect(client.getCollection("sleep")).resolves.toMatchObject({
+      nextToken: undefined,
+      records: [{ id: SLEEP.id }],
+    });
+  });
+
   it("rejects provider collection limits outside the whole-number range 1 through 25 before fetching", async () => {
     const fetchMock = vi.spyOn(globalThis, "fetch");
     const client = new WhoopClient(ENV, "access");
diff --git a/src/schemas/whoop.ts b/src/schemas/whoop.ts
index 916f1e0..bd1adb2 100644
--- a/src/schemas/whoop.ts
+++ b/src/schemas/whoop.ts
@@ -105,7 +105,7 @@ export const whoopWorkoutSchema = z.object({
 
 export const whoopCollectionResponseSchema = <T extends z.ZodTypeAny>(recordSchema: T) => z.object({
   records: z.array(recordSchema),
-  next_token: z.string().optional(),
+  next_token: z.string().nullish(),
 }).passthrough();
 
 export type WhoopWebhook = z.infer<typeof whoopWebhookSchema>;
diff --git a/src/services/whoop/client.ts b/src/services/whoop/client.ts
index 00f35e6..b3fd685 100644
--- a/src/services/whoop/client.ts
+++ b/src/services/whoop/client.ts
@@ -234,7 +234,7 @@ export class WhoopClient {
         record,
         rawRecords[index],
       )) as Array<WhoopProviderRecord<WhoopCollectionRecordMap[R]>>,
-      nextToken: parsed.data.next_token,
+      nextToken: parsed.data.next_token ?? undefined,
     };
   }