Index: target-i386/translate.c
--- target-i386/translate.c	8 Nov 2007 14:25:03 -0000	1.74
+++ target-i386/translate.c	18 Dec 2007 12:14:08 -0000
@@ -3887,7 +3887,7 @@
     case 0x1c7: /* cmpxchg8b */
         modrm = ldub_code(s->pc++);
         mod = (modrm >> 6) & 3;
-        if (mod == 3)
+        if ((mod == 3) || ((modrm & 0x38) != 0x8))
             goto illegal_op;
         gen_jmp_im(pc_start - s->cs_base);
         if (s->cc_op != CC_OP_DYNAMIC)