Operation on char* may be undefined

Question

I have this code that is warning me

Code :

int handle_operation(char *b) {
    char *buf = b;
    uint16_t opcode;
    memcpy(&opcode, buf, 2);
    buf = buf += 2;
}

Warning :

warning: operation on ‘buf’ may be undefined [-Wsequence-point]
   53 |     buf = buf++;

My goal is to increment the buffer's pointer by x each time I memcpy x bytes of it somewhere.