diff --git a/src/vs/platform/environment/common/environment.ts b/src/vs/platform/environment/common/environment.ts
index c64c5fc6815cec9555b678c10116c4b0c872c670..f899de2f91064dba0528a41b423901c49ffc0079 100644
--- a/src/vs/platform/environment/common/environment.ts
+++ b/src/vs/platform/environment/common/environment.ts
@@ -39,7 +39,7 @@ export interface IEnvironmentService {
 	// --- settings sync
 	userDataSyncLogResource: URI;
 	userDataSyncHome: URI;
-	sync: 'on' | 'off';
+	sync: 'on' | 'off' | undefined;
 
 	// --- extension development
 	debugExtensionHost: IExtensionHostDebugParams;
diff --git a/src/vs/platform/environment/node/environmentService.ts b/src/vs/platform/environment/node/environmentService.ts
index 4008fe2109a578c6caeae28e9f2e244593947b8e..695594fcb5872b10dad905a26f265b370b538de7 100644
--- a/src/vs/platform/environment/node/environmentService.ts
+++ b/src/vs/platform/environment/node/environmentService.ts
@@ -92,7 +92,7 @@ export class EnvironmentService implements INativeEnvironmentService {
 	get userDataSyncLogResource(): URI { return URI.file(path.join(this.logsPath, 'userDataSync.log')); }
 
 	@memoize
-	get sync(): 'on' | 'off' { return this.args.sync === 'off' ? 'off' : 'on'; }
+	get sync(): 'on' | 'off' | undefined { return this.args.sync; }
 
 	@memoize
 	get machineSettingsResource(): URI { return resources.joinPath(URI.file(path.join(this.userDataPath, 'Machine')), 'settings.json'); }