No Provider for FormBuilder

I'm still new to this and learning via tutorials, but for some reason i'm getting the message No provider for formbuilder when trying to test unique username. I'm not sure why i'm getting this message, but i'm unable to find a solution. Can anyone tell me why this is happening?

signup-component.ts

import {Component} from '@angular/core';
import {ControlGroup, Control, Validators, FormBuilder} from '@angular/common'
import {UsernameValidators} from './usernameValidators'

@Component({
selector: 'signup',
templateUrl: 'signup-component.html'

})
export class SignupComponent{
  form: ControlGroup;

  constructor(fb: FormBuilder){
    this.form = fb.group({
      username:['', Validators.compose([
          Validators.required, UsernameValidators.cannotContainSpace
      ])],
      password: ['', Validators.required]
    })
  }
}

usernameValidators.ts

import {Control} from '@angular/common'


export class UsernameValidators{

  static shouldBeUnique(control: Control){
    return new Promise((resolve, reject) => {
      setTimeout(function(){
        if(control.value == "andy")
          resolve({shouldBeUnique: true});
        else
          resolve(null);
      }, 1000);

    });

  }


  static cannotContainSpace(control: Control){
    if (control.value.indexOf(' ') >= 0)
      return {cannotContainSpace: true};

    return null;
  }
}

Import ReactiveFormsModule and FormsModule

@NgModule({
  imports: [
      BrowserModule /* or CommonModule */, 
      FormsModule, ReactiveFormsModule
  ],
  ...
})

in the module where you're using FormBuilder