sysntax error in subroutine

Code: Alles auswählen.

PROGRAM  zexample2.

DATA: var1 TYPE i.
WRITE:/ 'value before changing', var1.
PERFORM sub1 USING var1.
WRITE:/ 'value in after changing', var1.
*&---------------------------------------------------------------------*
*&      Form  sub1
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
*      -->P_VAR1  text
*----------------------------------------------------------------------*
FORM sub1  USING  value (p_var1).

  WRITE:/ 'value in subroutine before changing ', p_var1 .
  p_var1 = 999.
  WRITE:/ 'value in subroutine after changing ', p_var1 .

ENDFORM.                         " sub1

Code: Alles auswählen.

FORM sub1  USING  VALUE(p_var1).