diff --git a/src/logger.ts b/src/logger.ts
index d05ee26..714bbe1 100644
--- a/src/logger.ts
+++ b/src/logger.ts
@@ -1,4 +1,4 @@
-import type { FastifyReply, FastifyRequest } from 'fastify'
+import type { FastifyServerOptions } from 'fastify'
 import crypto from 'node:crypto'
 import pino from 'pino'
 import redactEnv from 'redact-env'
@@ -23,7 +23,7 @@ export function getLoggerOptions({
   name,
   redactEnv = [],
   redactLogPaths = []
-}: Options) {
+}: Options): FastifyServerOptions['logger'] {
   // todo: Move env redaction to a Pino v7+ Transport
   return {
     level:
@@ -48,25 +48,27 @@ export function getLoggerOptions({
       commit: process.env.COMMIT_ID?.slice(0, 8)
     },
     serializers: {
-      req(req: FastifyRequest) {
+      req(req) {
         return {
           method: req.method,
           url: req.url,
           headers: req.headers
         }
       },
-      res(res: FastifyReply) {
+      res(res) {
         return {
           statusCode: res.statusCode,
-          headers: res.getHeaders()
+          headers: res.getHeaders?.() ?? {}
         }
       }
     }
   }
 }
 
-export const makeReqIdGenerator = (defaultSalt: string = randomID()) =>
-  function genReqId(req: FastifyRequest): string {
+export const makeReqIdGenerator = (
+  defaultSalt: string = randomID()
+): FastifyServerOptions['genReqId'] =>
+  function genReqId(req) {
     let ipAddress: string = ''
     const xForwardedFor = req.headers['x-forwarded-for']
     if (xForwardedFor) {