diff --git a/src/vs/platform/configuration/common/userConfigurationFileService.ts b/src/vs/platform/configuration/common/userConfigurationFileService.ts
index 12245ff5e55..2507cb3e1f4 100644
--- a/src/vs/platform/configuration/common/userConfigurationFileService.ts
+++ b/src/vs/platform/configuration/common/userConfigurationFileService.ts
@@ -66,7 +66,7 @@ export class UserConfigurationFileService implements IUserConfigurationFileServi
 		if (edit) {
 			content = content.substring(0, edit.offset) + edit.content + content.substring(edit.offset + edit.length);
 			try {
-				await this.write(VSBuffer.fromString(content), { etag, mtime });
+				await this.fileService.writeFile(this.environmentService.settingsResource, VSBuffer.fromString(content), { etag, mtime });
 			} catch (error) {
 				if ((<FileOperationError>error).fileOperationResult === FileOperationResult.FILE_MODIFIED_SINCE) {
 					throw new Error(UserConfigurationErrorCode.ERROR_FILE_MODIFIED_SINCE);
@@ -76,7 +76,10 @@ export class UserConfigurationFileService implements IUserConfigurationFileServi
 	}
 
 	async write(content: VSBuffer, options?: IWriteFileOptions): Promise<void> {
-		await this.fileService.writeFile(this.environmentService.settingsResource, content, options);
+		// queue up writes to prevent race conditions
+		return this.queue.queue(async () => {
+			await this.fileService.writeFile(this.environmentService.settingsResource, content, options);
+		});
 	}
 
 	private getEdits({ value, path }: IJSONValue, modelContent: string, formattingOptions: FormattingOptions): Edit[] {
diff --git a/src/vs/platform/userDataSync/test/common/userDataSyncClient.ts b/src/vs/platform/userDataSync/test/common/userDataSyncClient.ts
index 99fb6c02c0c..cf3e6333d88 100644
--- a/src/vs/platform/userDataSync/test/common/userDataSyncClient.ts
+++ b/src/vs/platform/userDataSync/test/common/userDataSyncClient.ts
@@ -16,6 +16,7 @@ import { generateUuid } from 'vs/base/common/uuid';
 import { IHeaders, IRequestContext, IRequestOptions } from 'vs/base/parts/request/common/request';
 import { IConfigurationService } from 'vs/platform/configuration/common/configuration';
 import { ConfigurationService } from 'vs/platform/configuration/common/configurationService';
+import { IUserConfigurationFileService, UserConfigurationFileService } from 'vs/platform/configuration/common/userConfigurationFileService';
 import { IEnvironmentService } from 'vs/platform/environment/common/environment';
 import { GlobalExtensionEnablementService } from 'vs/platform/extensionManagement/common/extensionEnablementService';
 import { DidUninstallExtensionEvent, IExtensionGalleryService, IExtensionManagementService, IGlobalExtensionEnablementService, InstallExtensionResult } from 'vs/platform/extensionManagement/common/extensionManagement';
@@ -88,6 +89,7 @@ export class UserDataSyncClient extends Disposable {
 		const configurationService = this._register(new ConfigurationService(environmentService.settingsResource, fileService));
 		await configurationService.initialize();
 		this.instantiationService.stub(IConfigurationService, configurationService);
+		this.instantiationService.stub(IUserConfigurationFileService, this.instantiationService.createInstance(UserConfigurationFileService));
 
 		this.instantiationService.stub(IRequestService, this.testServer);