$ cat a.asm .code16 data32 push 8 data32 push 9 $ llvm-mc --show-encoding --x86-asm-syntax=intel a.asm .code16 pushw $8 # encoding: [0x6a,0x08] data32 # encoding: [0x66] pushw $9 # encoding: [0x6a,0x09] Happens only with intel syntax.