Internal procedure not allowed as actual argument

[Janus Weil]

Hi all,
I have a question: why doesn't gfortran allow passing an internal
procedure as an argument to another procedure, as in this example:


subroutine sub

  call proc(f1)
  call proc(f2)

  contains

  real function f1(x)
  ...
  end function f1

end subroutine sub


real function f2(x)
 ...
end function f2


If we have a subroutine "proc" that expects an external function as
its argument, "call proc(f2)" is allowed by gfortran, while "call
proc(f1)" triggers an error like this:

Error: Internal procedure 'f1' is not allowed as an actual argument at (1)

g95 shows the same behaviour, but ifort doesn't complain about this at all.
Can anyone tell me what the reason for this restriction is?
Thanks,
Janus