Bitfeld an PORTD zuweisen

Hallo

struct{
  unsigned char on_left:1;
  unsigned char on_right:1;
  unsigned char long_left:1;
  unsigned char long_right:1;
  unsigned char up:1;
  unsigned char longup:1;
} flags_servos;

PORTB = (uint8_t)flags_servos;

Der Compiler meint dazu:

error: aggregate value used where an integer was expected

Wie kann ich das zum Laufen brigen? Ich will also das Bitfeld direkt
nach PORTD bringen.

Gruss

Michael