Ninject multiple binding of injected interface

I have the following classes:

using System;

interface IA { }

class A1 : IA { }

class A2 : IA { }

class B
{
    public B(IA a) {}
}

class BProvider : Provider<B>
{
    IA _a;

    public BProvider(IA a) { _a=a; }

    protected override B CreateInstance(IContext context) { return new B(_a); }
}

ninject module Load() code:

Bind<IA>().To<A1>();
Bind<IA>().To<A2>();
Bind<B>().ToProvider<BProvider>();

main code:

kernel.GetAll<IA>(); // works fine
kernel.GetAll<B>(); // I expect to get IEnumerable<B> with two elements, but instead of this I get an error that there are multiple bindings of IA and ninject cannot determine which to use

So the question is if I can make the last statement work as expected or do it some other way?