bits 64 add [rax], dword 4 ; illegal; must use dword [eax], 4 add [rax], strict dword 4 ; illegal; must use dword [eax], strict dword 4 add [rax], qword 4 ; illegal; must use qword [rax], 4 add [rax], strict qword 4 ; illegal; must use qword [eax], strict dword 4