diff --git a/lib/getServerSideProps.ts b/lib/getServerSideProps.ts
index 94a24f9..bfafe67 100644
--- a/lib/getServerSideProps.ts
+++ b/lib/getServerSideProps.ts
@@ -1,7 +1,14 @@
-import { GetServerSideProps } from 'next'
 import { getBookingByUUID } from '../db/index'
 
-export const getServerSideBooking: GetServerSideProps = async (context) => {
+export interface ServerSideBooking {
+  props: {
+    booking: object
+  }
+}
+
+export const getServerSideBooking = async (
+  context: any
+): Promise<ServerSideBooking> => {
   const {
     res,
     params: { uuid: uuids },
@@ -12,14 +19,14 @@ export const getServerSideBooking: GetServerSideProps = async (context) => {
   if (!booking) {
     res.statusCode = 404
     res.end()
-    return { props: {} }
+    return { props: { booking: null } }
   }
 
   await booking.populate('booker').execPopulate()
   await booking.populate('bill').execPopulate()
 
   // TODO: hack, not sure why _id is not serilizable
-  const bookingJSON = JSON.parse(JSON.stringify(booking.toJSON()))
+  const bookingJSON = JSON.parse(JSON.stringify(booking.toJSON())) as object
   return {
     props: { booking: bookingJSON },
   }
diff --git a/lib/session.ts b/lib/session.ts
index 6c35c15..8d3ed88 100644
--- a/lib/session.ts
+++ b/lib/session.ts
@@ -1,6 +1,15 @@
 import { withIronSession, Handler } from 'next-iron-session'
 import { getBaseURL } from '../helpers/url'
 
+export enum USER_ROLE {
+  ADMIN = 'admin',
+}
+
+export interface UserData {
+  username: string
+  role: USER_ROLE
+}
+
 const SESSION_SECRET =
   process.env.SESSION_SECRET || 'dev-env-default-secret-991823723'
 
@@ -16,13 +25,13 @@ export default function withSession(handler: Handler) {
   })
 }
 
-export function isAdminSession(req: any, res: any) {
-  const user = req?.session.get('user')
-  if (user && user.role === 'admin') {
+export function isAdminSession(req: any) {
+  const user = req?.session.get('user') as UserData
+  if (user && user.role === USER_ROLE.ADMIN) {
     return user
   }
 
-  return false
+  return null
 }
 
 export function redirectToLogin(req: any, res: any) {
diff --git a/pages/admin/booking/[uuid]/bill.tsx b/pages/admin/booking/[uuid]/bill.tsx
index 93d4a43..c14017f 100644
--- a/pages/admin/booking/[uuid]/bill.tsx
+++ b/pages/admin/booking/[uuid]/bill.tsx
@@ -1,5 +1,4 @@
 import React, { useEffect, useState } from 'react'
-import { GetServerSideProps } from 'next'
 import Footer from '../../../../components/footer'
 import Header from '../../../../components/header'
 import Input from '../../../../components/input'
@@ -17,27 +16,26 @@ import withSession, {
 } from '../../../../lib/session'
 import { getServerSideBooking } from '../../../../lib/getServerSideProps'
 
-export const getServerSideProps: GetServerSideProps = withSession(
-  async (context) => {
-    const { req, res } = context
+export const getServerSideProps = withSession(async (context) => {
+  const { req, res } = context
 
-    const adminUser = isAdminSession(req, res)
+  const adminUser = isAdminSession(req)
 
-    if (!adminUser) {
-      redirectToLogin(req, res)
-      return { props: {} }
-    }
-
-    const milageMax = await getMilageMax()
-    const result = await getServerSideBooking(context)
-    return {
-      ...result,
-      // TODO: have a closer look at this type issue. Seems like a bug
-      // @ts-ignore
-      props: { ...result.props, milageMax, user: adminUser },
-    }
+  if (!adminUser) {
+    redirectToLogin(req, res)
+    return { props: {} }
   }
-)
+
+  const milageMax = await getMilageMax()
+  const serverSideBookingProps = await getServerSideBooking(context)
+  return {
+    props: {
+      ...serverSideBookingProps.props.booking,
+      milageMax,
+      user: adminUser,
+    },
+  }
+})
 
 const milageTarifOptions = Object.values(MILAGE_TARIFS).map((tarif) => {
   return (
diff --git a/pages/admin/booking/[uuid]/index.tsx b/pages/admin/booking/[uuid]/index.tsx
index 7106364..6c3dae9 100644
--- a/pages/admin/booking/[uuid]/index.tsx
+++ b/pages/admin/booking/[uuid]/index.tsx
@@ -17,7 +17,7 @@ export const getServerSideProps: GetServerSideProps = withSession(
   async (context) => {
     const { req, res } = context
 
-    const adminUser = isAdminSession(req, res)
+    const adminUser = isAdminSession(req)
 
     if (!adminUser) {
       redirectToLogin(req, res)