diff --git a/match_collector/index.ts b/match_collector/index.ts
index 48285f8..c3839ff 100644
--- a/match_collector/index.ts
+++ b/match_collector/index.ts
@@ -5,6 +5,7 @@ const sleep_minutes = 12
 import { MongoClient } from 'mongodb'
 
 import champion_stat from './champion_stat'
+import { Match } from './api'
 
 main()
 
@@ -32,7 +33,7 @@ async function main() {
     const challengerLeague = await fetchChallengerLeague()
     console.log('ChallengerLeague: got ' + challengerLeague.entries.length + ' entries')
 
-    const gameList = []
+    const gameList : string[] = []
     let i = 0
     for (const challenger of challengerLeague.entries) {
       console.log('Entry ' + i + '/' + challengerLeague.entries.length + ' ...')
@@ -105,11 +106,11 @@ async function connectToDatabase() {
   return client
 }
 
-async function fetchLatestPatchDate(client) {
+async function fetchLatestPatchDate(client: MongoClient) {
   const database = client.db('patches')
   const patches = database.collection('patches')
   const latestPatch = await patches.find().limit(1).sort({ date: -1 }).next()
-  return [latestPatch.patch, Math.floor(latestPatch.date.valueOf() / 1000)]
+  return [latestPatch!.patch, Math.floor(latestPatch!.date.valueOf() / 1000)]
 }
 
 async function fetchChallengerLeague() {
@@ -125,7 +126,7 @@ async function fetchChallengerLeague() {
   return challengerLeague
 }
 
-async function summonerGameList(puuid, startTime) {
+async function summonerGameList(puuid: string, startTime: string) {
   const base = 'https://europe.api.riotgames.com'
   const endpoint = `/lol/match/v5/matches/by-puuid/${puuid}/ids`
   const url = `${base}${endpoint}?queue=420&type=ranked&startTime=${startTime}&api_key=${api_key}`
@@ -137,7 +138,7 @@ async function summonerGameList(puuid, startTime) {
   return gameList
 }
 
-async function match(matchId) {
+async function match(matchId: string) {
   const base = 'https://europe.api.riotgames.com'
   const endpoint = `/lol/match/v5/matches/${matchId}`
   const url = `${base}${endpoint}?api_key=${api_key}`
@@ -149,7 +150,7 @@ async function match(matchId) {
   return match
 }
 
-async function matchTimeline(matchId) {
+async function matchTimeline(matchId: string) {
   const base = 'https://europe.api.riotgames.com'
   const endpoint = `/lol/match/v5/matches/${matchId}/timeline`
   const url = `${base}${endpoint}?api_key=${api_key}`
@@ -161,7 +162,7 @@ async function matchTimeline(matchId) {
   return timeline
 }
 
-async function alreadySeenGames(client, latestPatch) {
+async function alreadySeenGames(client: MongoClient, latestPatch: string) {
   const database = client.db('matches')
   const matches = database.collection(latestPatch)
 
@@ -169,7 +170,7 @@ async function alreadySeenGames(client, latestPatch) {
   return alreadySeen
 }
 
-async function saveMatch(client, match, latestPatch) {
+async function saveMatch(client: MongoClient, match: Match, latestPatch: string) {
   const database = client.db('matches')
   const matches = database.collection(latestPatch)
   await matches.insertOne(match)