Makefile and code - illegal fortran syntax?

Makefile

.PHONY: all pgi intel gcc nag clean

all: gcc intel nag pgi

pgi:
        pgfortran -V
        pgfortran -Minform=inform -Mbounds intertest.f90 -o intertest-pgi
        ./intertest-pgi

intel:
        ifort -V
        ifort -warn -check intertest.f90 -o intertest-intel
        ./intertest-intel

nag:
        nagfor -V
        nagfor intertest.f90 -o intertest-nag
        ./intertest-nag

gcc:
        gcc --version
        gfortran -Wall -Wextra -fcheck=all intertest.f90 -o intertest-gcc
        ./intertest-gcc

clean:
        rm -f *.mod intertest-pgi intertest-gcc intertest-intel

module intertest
    implicit none

    type beta
        real :: val
    end type beta

    interface beta
        module procedure :: beta_constructor
    end interface beta

contains

    function beta_constructor(val) result(this)
        implicit none
        type(beta) :: this
        real, intent(in) :: val

        this%val = val
    end function beta_constructor

end module intertest


program test_interface
    use intertest
    implicit none

    type(beta) :: b

    b = beta(3.14)
    print *, "If this prints 3.14, all is OK: ", b%val
end program test_interface