Dummy arguments of separate (sub) module procedure not declared

[LKedward]

module m
  implicit none
  interface
    module subroutine sub1(a)
      integer :: a
    end subroutine sub1
  end interface
end module m

submodule (m) sm
  implicit none
  contains
    module procedure sub1
      write(*,*) a
    end procedure sub1
end submodule sm

This is giving semantic error:

error: No explicit type declared for 'a'