diff --git a/examples/with-mongodb/lib/mongodb.ts b/examples/with-mongodb/lib/mongodb.ts
index 7aaf63e04cec..9397929118bb 100644
--- a/examples/with-mongodb/lib/mongodb.ts
+++ b/examples/with-mongodb/lib/mongodb.ts
@@ -8,7 +8,7 @@ const uri = process.env.MONGODB_URI
 const options = {}
 
 let client
-let clientPromise
+let clientPromise: Promise<MongoClient>
 
 if (!process.env.MONGODB_URI) {
   throw new Error('Please add your Mongo URI to .env.local')