How to printf a 64-bit integer as hex?

With the following code I am trying to output the value of a unit64_t variable using printf(). Compiling the code with gcc, returns the following warning:

warning: format ‘%x’ expects argument of type ‘unsigned int’, but argument 2 has type ‘uint64_t’ [-Wformat=]

The code:

#include <stdio.h>
#include <stdint.h>

int main ()
{
    uint64_t val = 0x1234567890abcdef;
    printf("val = 0x%x\n", val);

    return 0;
}

The output:

val = 0x90abcdef

Expected output:

val = 0x1234567890abcdef

How can I output a 64bit value as a hexadecimal integer using printf()? The x specifier seems to be wrong in this case.