diff --git a/packages/app-store/office365calendar/lib/CalendarService.ts b/packages/app-store/office365calendar/lib/CalendarService.ts
index 63bfee84d3..a15da00f1d 100644
--- a/packages/app-store/office365calendar/lib/CalendarService.ts
+++ b/packages/app-store/office365calendar/lib/CalendarService.ts
@@ -1,4 +1,5 @@
 import type { Calendar as OfficeCalendar, User } from "@microsoft/microsoft-graph-types-beta";
+import { z } from "zod";
 
 import dayjs from "@calcom/dayjs";
 import { getLocation, getRichDescription } from "@calcom/lib/CalEventParser";
@@ -38,6 +39,14 @@ interface IBatchResponse {
   responses: ISettledResponse[];
 }
 
+const refreshTokenResponseSchema = z.object({
+  access_token: z.string(),
+  expires_in: z
+    .number()
+    .transform((currentTimeOffsetInSeconds) => Math.round(+new Date() / 1000 + currentTimeOffsetInSeconds)),
+  refresh_token: z.string().optional(),
+});
+
 export default class Office365CalendarService implements Calendar {
   private url = "";
   private integrationName = "";
@@ -217,14 +226,7 @@ export default class Office365CalendarService implements Calendar {
           client_secret,
         }),
       });
-      const responseBody = await handleErrorsJson<{
-        access_token: string;
-        expires_in: number;
-        refresh_token: string;
-      }>(response);
-      o365AuthCredentials.access_token = responseBody.access_token;
-      o365AuthCredentials.refresh_token = responseBody.refresh_token;
-      o365AuthCredentials.expiry_date = Math.round(+new Date() / 1000 + responseBody.expires_in);
+      const o365AuthCredentials = refreshTokenResponseSchema.parse(await handleErrorsJson(response));
       await prisma.credential.update({
         where: {
           id: credential.id,