gfortran Unclassifiable statment for type-bound loop variable

Is there a reason this produces an unclassifiable statement error on the line "do my_a%i = 1, 5"?

mymod.f90

module mymod                                                                                                                          
   type a                                                                                                                             
      integer :: i                                                                                                                    
   end type a                                                                                                                         
end module mymod 

main.f90

program main                                                                                                                          
   use mymod, only : a                                                                                                                
   implicit none                                                                                                                      
   type(a) :: my_a                                                                                                                       
                                                                                                                                      
                                                                                                                                      
   do my_a%i = 1, 5                                                                                                                      
      print *, "hello"                                                                                                                
   enddo                                                                                                                              
end program main