diff --git a/lib/Target/X86/X86CodeEmitter.cpp b/lib/Target/X86/X86CodeEmitter.cpp
index 135ef7844e1..d9ca7d94583 100644
--- a/lib/Target/X86/X86CodeEmitter.cpp
+++ b/lib/Target/X86/X86CodeEmitter.cpp
@@ -372,6 +372,14 @@ void Emitter::emitInstruction(const MachineInstr &MI) {
     MCE.emitByte(0x0F);   // Two-byte opcode prefix
     break;
   case X86II::REP: break; // already handled.
+  case X86II::XS:   // F3 0F
+    MCE.emitByte(0xF3);
+    MCE.emitByte(0x0F);
+    break;
+  case X86II::XD:   // F2 0F
+    MCE.emitByte(0xF2);
+    MCE.emitByte(0x0F);
+    break;
   case X86II::D8: case X86II::D9: case X86II::DA: case X86II::DB:
   case X86II::DC: case X86II::DD: case X86II::DE: case X86II::DF:
     MCE.emitByte(0xD8+