diff --git a/clang/Basic/Targets.cpp b/clang/Basic/Targets.cpp
index cede59858a37..e8238daeae39 100644
--- a/clang/Basic/Targets.cpp
+++ b/clang/Basic/Targets.cpp
@@ -486,7 +486,9 @@ namespace X86 {
     case 't': // top of floating point stack.
     case 'u': // second from top of floating point stack.
     case 'q': // a, b, c, d registers or any integer register in 64-bit.
-    case 'Z': // 32-bit integer constant for used with zero-extending x86_64
+    case 'Z': // 32-bit integer constant for use with zero-extending x86_64
+              // instructions.
+    case 'N': // unsigned 8-bit integer constant for use with in and out
               // instructions.
       info = (TargetInfo::ConstraintInfo)(info|TargetInfo::CI_AllowsRegister);
       return true;