in drone.h

I have a struct

typedef struct {
  char name[MAX_DRONE_NAME_LENGTH];
  enum drone_model model;
  uint8_t status_bitarr;
} drone;

and a define

#define DRONE_STATUS_LENGTH (8*sizeof( ((drone*)0)->status_bitarr ))

I can use the value of this define, as well as the original expression in main.c

printf("%d\n", (8*sizeof( ((drone*)0)->status_bitarr )) );
printf("%d\n", DRONE_STATUS_LENGTH);
static char bob[DRONE_STATUS_LENGTH]="aaaaaaaa";
printf("%c\n", bob[2]);

8
8
a

but in drone.c the line

 static char result[DRONE_STATUS_LENGTH];

produces an "expected expression error"

./drone.c:34:22: error: expected expression
  static char result[DRONE_STATUS_LENGTH]={0};
                     ^
./drone.h:24:48: note: expanded from macro 'DRONE_STATUS_LENGTH'
#define DRONE_STATUS_LENGTH (8*sizeof( ((drone*)0)->status_bitarr ))

replacing with a hardcoded value fixes error, but I want to use sizeof

how do I get it to work?

C, sizeof, array, c macro, c defines