diff --git a/llvm/lib/Target/X86/X86InstrSystem.td b/llvm/lib/Target/X86/X86InstrSystem.td
--- a/llvm/lib/Target/X86/X86InstrSystem.td
+++ b/llvm/lib/Target/X86/X86InstrSystem.td
@@ -584,7 +584,7 @@
 //===----------------------------------------------------------------------===//
 // VIA PadLock crypto instructions
 let Defs = [RAX, RDI], Uses = [RDX, RDI], SchedRW = [WriteSystem] in
-  def XSTORE : I<0xa7, MRM_C0, (outs), (ins), "xstore", []>, TB, REP;
+  def XSTORE : I<0xa7, MRM_C0, (outs), (ins), "xstore", []>, TB;
 
 def : InstAlias<"xstorerng", (XSTORE)>;
 
diff --git a/llvm/test/MC/X86/padlock.s b/llvm/test/MC/X86/padlock.s
--- a/llvm/test/MC/X86/padlock.s
+++ b/llvm/test/MC/X86/padlock.s
@@ -1,8 +1,11 @@
 // RUN: llvm-mc -triple i386-unknown-unknown --show-encoding %s | FileCheck %s
 
+/// Check xstore does not get an implicit REP prefix but all other PadLock
+/// instructions do.
+
 	xstore
 // CHECK: xstore
-// CHECK: encoding: [0xf3,0x0f,0xa7,0xc0]
+// CHECK: encoding: [0x0f,0xa7,0xc0]
 	xcryptecb
 // CHECK: xcryptecb
 // CHECK: encoding: [0xf3,0x0f,0xa7,0xc8]