diff --git a/lib/Target/X86/X86InstrInfo.td b/lib/Target/X86/X86InstrInfo.td
index 7a4e796cadb..4f3a3af0f97 100644
--- a/lib/Target/X86/X86InstrInfo.td
+++ b/lib/Target/X86/X86InstrInfo.td
@@ -2594,7 +2594,7 @@ def LCMPXCHG32 : I<0xB1, MRMDestMem, (outs), (ins i32mem:$ptr, GR32:$swap),
                [(X86cas addr:$ptr, GR32:$swap, 4)]>, TB, LOCK;
 }
 let Defs = [EAX, EBX, ECX, EDX, EFLAGS], Uses = [EAX, EBX, ECX, EDX] in {
-def LCMPXCHG8B : I<0xC7, MRMDestMem, (outs), (ins i32mem:$ptr),
+def LCMPXCHG8B : I<0xC7, MRM1m, (outs), (ins i32mem:$ptr),
                "lock cmpxchg8b\t$ptr",
                [(X86cas8 addr:$ptr)]>, TB, LOCK;
 }