TypeScript Version: 2.5.2

Code

interface ITypeChecker
{
    isOfType<T extends TBase, TBase>(obj: TBase): obj is T; 
}


class Checker implements ITypeChecker
{
    isOfType<T extends TBase, TBase>(obj: TBase): obj is T
    {
        return true;
    }

}

Expected behavior:
Class Checker should be treated as a valid implementation (used to be in Ts-2.3).
Actual behavior:
Compiler complains:

• interface-not-properly-implemented
  (...)
  • Type predicate 'value is TBase' is not assignable to 'value is T'
    • Type 'TBase' is not assignable to type 'T'