AngularFirstore未定义

我正在用angularfire和firebase做一个简单的角度应用程序。但我对Angularfire有个问题。控制台上的错误显示:

Uncaught ReferenceError: AngularFirstore is not defined

    at eval (app.module.ts:15)
    at eval (app.module.ts:18)

我的 应用程序。modudule。ts 是

import { BrowserModule } from "@angular/platform-browser";
import { NgModule } from "@angular/core";
import { AppComponent } from "./app.component";
import { AngularFireModule } from "angularfire2";
import { environment } from "../environments/environment";
import { AngularFirestore } from 'angularfire2/firestore';


@NgModule({
  imports: [
    BrowserModule,
    AngularFireModule.initializeApp(environment.firebase)
  ],
  declarations: [AppComponent],
  providers: [AngularFirstore],
  bootstrap: [AppComponent]
})
export class AppModule {}