diff --git a/src/routes/api/sync.js b/src/routes/api/sync.js
index 4cac6ffb5..0d68827e1 100644
--- a/src/routes/api/sync.js
+++ b/src/routes/api/sync.js
@@ -6,7 +6,7 @@ const entityChangesService = require('../../services/entity_changes');
 const sql = require('../../services/sql');
 const sqlInit = require('../../services/sql_init');
 const optionService = require('../../services/options');
-const contentHashService = require('../../services/content_hash.js');
+const contentHashService = require('../../services/content_hash');
 const log = require('../../services/log');
 const syncOptions = require('../../services/sync_options');
 const utils = require('../../services/utils');
diff --git a/src/services/content_hash.js b/src/services/content_hash.ts
similarity index 79%
rename from src/services/content_hash.js
rename to src/services/content_hash.ts
index 24fbfcfaa..2067e177f 100644
--- a/src/services/content_hash.js
+++ b/src/services/content_hash.ts
@@ -1,9 +1,11 @@
 "use strict";
 
-const sql = require('./sql');
-const utils = require('./utils');
-const log = require('./log');
-const eraseService = require('./erase');
+import sql = require('./sql');
+import utils = require('./utils');
+import log = require('./log');
+import eraseService = require('./erase');
+
+type SectorHash = Record<string, string>;
 
 function getEntityHashes() {
     // blob erasure is not synced, we should check before each sync if there's some blob to erase
@@ -12,8 +14,9 @@ function getEntityHashes() {
     const startTime = new Date();
 
     // we know this is slow and the total content hash calculation time is logged
+    type HashRow = [ string, string, string, boolean ];
     const hashRows = sql.disableSlowQueryLogging(
-        () => sql.getRawRows(`
+        () => sql.getRawRows<HashRow>(`
             SELECT entityName,
                    entityId,
                    hash,
@@ -27,7 +30,7 @@ function getEntityHashes() {
     // sorting by entityId is enough, hashes will be segmented by entityName later on anyway
     hashRows.sort((a, b) => a[1] < b[1] ? -1 : 1);
 
-    const hashMap = {};
+    const hashMap: Record<string, SectorHash> = {};
 
     for (const [entityName, entityId, hash, isErased] of hashRows) {
         const entityHashMap = hashMap[entityName] = hashMap[entityName] || {};
@@ -51,13 +54,13 @@ function getEntityHashes() {
     return hashMap;
 }
 
-function checkContentHashes(otherHashes) {
+function checkContentHashes(otherHashes: Record<string, SectorHash>) {
     const entityHashes = getEntityHashes();
     const failedChecks = [];
 
     for (const entityName in entityHashes) {
-        const thisSectorHashes = entityHashes[entityName] || {};
-        const otherSectorHashes = otherHashes[entityName] || {};
+        const thisSectorHashes: SectorHash = entityHashes[entityName] || {};
+        const otherSectorHashes: SectorHash = otherHashes[entityName] || {};
 
         const sectors = new Set(Object.keys(thisSectorHashes).concat(Object.keys(otherSectorHashes)));
 
@@ -77,7 +80,7 @@ function checkContentHashes(otherHashes) {
     return failedChecks;
 }
 
-module.exports = {
+export = {
     getEntityHashes,
     checkContentHashes
 };
diff --git a/src/services/sync.js b/src/services/sync.js
index dba9d13a0..a935e1de8 100644
--- a/src/services/sync.js
+++ b/src/services/sync.js
@@ -7,7 +7,7 @@ const utils = require('./utils');
 const instanceId = require('./instance_id');
 const dateUtils = require('./date_utils');
 const syncUpdateService = require('./sync_update');
-const contentHashService = require('./content_hash.js');
+const contentHashService = require('./content_hash');
 const appInfo = require('./app_info');
 const syncOptions = require('./sync_options');
 const syncMutexService = require('./sync_mutex');