Backwards compatibility between intel 18 and intel 17 ifort compilers

Hi,

I'm using ifort (intel 18) to compile this module:

     module test
     integer:: a
     contains
       subroutine f()
       end subroutine
     end module test

To be used with this program compiled with ifort (intel 17):

     program ping
     use test
     write ( *, '(a)' ) '  Hello, world!'
     end

But I am getting this error:

test.f90(2): error #7012: The module file cannot be read.  Its format requires a more recent F90 compiler.   [TEST]
      use test
----------^

However, I can compile the module with ifort (intel17) and then 'use' it in a program compiled with ifort (intel18) without any issues.

So, it it looks like the fortran modules are forwards compatible, but not backwards compatible between ifort compiler versions. Is there anything that I can do to get the module to work in the backwards compatible case?

Thanks,
Nick