Why doesn't getrandom() compile?

Silly question, I'm probably missing a header, but the man page says I just need #include <linux/random.h>.

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <linux/random.h>

#define BITS 8192
#define BYTES (BITS >> 3)

int main() {
    uint8_t array[BYTES];

    printf("started...");
    int r = getrandom(array, BYTES, 0);
    if (r) exit(1);

    return 0;
}

Error is:

chris@purple:~/lunch/bitarray$ make && ./bitarray 
clang -g -Wall -Wpedantic -Werror -std=c11 -O2 -save-temps bitarray.c -o bitarray
bitarray.c:13:10: error: implicit declaration of function 'getrandom' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
 int r = getrandom(array, (8192 >> 3), 0);
         ^
1 error generated.
Makefile:10: recipe for target 'bitarray' failed
make: *** [bitarray] Error 1

(Also fails in gcc.)

chris@purple:~/lunch/bitarray$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.2 LTS"
chris@purple:~/lunch/bitarray$ uname -a
Linux purple 4.4.0-83-generic #106-Ubuntu SMP Mon Jun 26 17:54:43 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux