The following program generates bogus errors compiling with current gfortran:

MODULE X

  USE ISO_C_BINDING
  INTERFACE
    REAL(KIND=C_FLOAT) FUNCTION mytype( a ) BIND(C)
       USE ISO_C_BINDING
       INTEGER(KIND=C_INT), VALUE :: a
    END FUNCTION
    SUBROUTINE init() BIND(C,name="init")
    END SUBROUTINE
  END INTERFACE

  TYPE(C_FUNPTR), BIND(C,name="funpointer") :: funpointer

END MODULE X

USE X
CALL init()
END