diff --git a/lib/Target/X86/AsmParser/X86AsmParser.cpp b/lib/Target/X86/AsmParser/X86AsmParser.cpp
index b6660710bbf..1b4086b41a8 100644
--- a/lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ b/lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -708,7 +708,7 @@ ParseInstruction(StringRef Name, SMLoc NameLoc,
     Name == "lock" || Name == "rep" ||
     Name == "repe" || Name == "repz" ||
     Name == "repne" || Name == "repnz" ||
-    Name == "rex64";
+    Name == "rex64" || Name == "data16";
 
 
   // This does the actual operand parsing.  Don't parse any more if we have a
diff --git a/lib/Target/X86/X86InstrInfo.td b/lib/Target/X86/X86InstrInfo.td
index d7a55057c4b..560cafe0816 100644
--- a/lib/Target/X86/X86InstrInfo.td
+++ b/lib/Target/X86/X86InstrInfo.td
@@ -1147,6 +1147,9 @@ def LOCK_PREFIX : I<0xF0, RawFrm, (outs),  (ins), "lock", []>;
 // Rex64 instruction prefix
 def REX64_PREFIX : I<0x48, RawFrm, (outs),  (ins), "rex64", []>;
 
+// Data16 instruction prefix
+def DATA16_PREFIX : I<0x66, RawFrm, (outs),  (ins), "data16", []>;
+
 // Repeat string operation instruction prefixes
 // These uses the DF flag in the EFLAGS register to inc or dec ECX
 let Defs = [ECX], Uses = [ECX,EFLAGS] in {
diff --git a/test/MC/X86/x86-64.s b/test/MC/X86/x86-64.s
index c8b8b244113..17f00faafc0 100644
--- a/test/MC/X86/x86-64.s
+++ b/test/MC/X86/x86-64.s
@@ -910,3 +910,4 @@ movq	%rax, %mm5 // CHECK: movd %rax, %mm5 # encoding: [0x48,0x0f,0x6e,0xe8]
 movq	%mm5, %rbx // CHECK: movd %mm5, %rbx # encoding: [0x48,0x0f,0x7e,0xeb]
 
 rex64 // CHECK: rex64 # encoding: [0x48]
+data16 // CHECK: data16 # encoding: [0x66]