Subscriber is null when injected in Aurelia class?

I have the following subscriber (in aSubscriber.js):

import {EventAggregator} from 'aurelia-event-aggregator';

export class Subscriber{
   static inject = [EventAggregator];
   constructor(eventAggregator){
    this.eventAggregator = eventAggregator;
   }

   subscribe(){
       this.eventAggregator.subscribe('myPublishChannelName', payload => {
        //do something with the payload here
        alert('got the message that has been published');
    });
  }

}

And in my class to register the subscriber I have:

import {inject} from 'aurelia-framework';
import {subscriber} from './aSubscriber';

 @inject(subscriber)    
 export class Welcome{

 constructor(subscriber){
    // this.subscriber = subscriber;
    // this.subscriber.subscribe(); 
  }   

}

In the constructor subscriber is undefined. Why is this happening?