diff --git a/src/abstractions/sync.service.ts b/src/abstractions/sync.service.ts
index 553124a27a9..a3287c39c9c 100644
--- a/src/abstractions/sync.service.ts
+++ b/src/abstractions/sync.service.ts
@@ -1,9 +1,9 @@
 export interface SyncService {
     syncInProgress: boolean;
 
-    getLastSync();
-    setLastSync(date: Date);
-    syncStarted();
-    syncCompleted(successfully: boolean);
-    fullSync(forceSync: boolean);
+    getLastSync(): Promise<Date>;
+    setLastSync(date: Date): Promise<any>;
+    syncStarted(): void;
+    syncCompleted(successfully: boolean): void;
+    fullSync(forceSync: boolean): Promise<boolean>;
 }
diff --git a/src/services/sync.service.ts b/src/services/sync.service.ts
index 550974c4ba7..79e726c9aa0 100644
--- a/src/services/sync.service.ts
+++ b/src/services/sync.service.ts
@@ -33,7 +33,7 @@ export class SyncService implements SyncServiceInterface {
         private messagingService: MessagingService, private logoutCallback: Function) {
     }
 
-    async getLastSync() {
+    async getLastSync(): Promise<Date> {
         const userId = await this.userService.getUserId();
         const lastSync = await this.storageService.get<any>(Keys.lastSyncPrefix + userId);
         if (lastSync) {
@@ -43,7 +43,7 @@ export class SyncService implements SyncServiceInterface {
         return null;
     }
 
-    async setLastSync(date: Date) {
+    async setLastSync(date: Date): Promise<any> {
         const userId = await this.userService.getUserId();
         await this.storageService.save(Keys.lastSyncPrefix + userId, date.toJSON());
     }
@@ -58,7 +58,7 @@ export class SyncService implements SyncServiceInterface {
         this.messagingService.send('syncCompleted', { successfully: successfully });
     }
 
-    async fullSync(forceSync: boolean) {
+    async fullSync(forceSync: boolean): Promise<boolean> {
         this.syncStarted();
         const isAuthenticated = await this.userService.isAuthenticated();
         if (!isAuthenticated) {