DDD - Invariant enforcement using instance methods and a factory method

I'm designing a system using Domain-Driven design principals.
I have an aggregate named Album.
It contains a collection of Tracks.
Album instances are created using a factory method named create(props).
Rule 1: An Album must contain at least one Track.
This rule must be checked upon creation (in Album.create(props)).
Also, there must a method named addTrack(track: Track) so that a new Track can be added after the instance is created. That means addTrack(track: Track) must check the rule too.
How can I avoid this logic code duplication?