diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 3596337c245e..77b46ae5cccb 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -580,7 +580,11 @@ IdentifierInfo *Preprocessor::LookUpIdentifierInfo(Token &Identifier) const {
 
   // Update the token info (identifier info and appropriate token kind).
   Identifier.setIdentifierInfo(II);
-  Identifier.setKind(II->getTokenID());
+  if (getLangOpts().MSVCCompat && II->isCPlusPlusOperatorKeyword() &&
+      getSourceManager().isInSystemHeader(Identifier.getLocation()))
+    Identifier.setKind(clang::tok::identifier);
+  else
+    Identifier.setKind(II->getTokenID());
 
   return II;
 }
diff --git a/clang/test/Headers/ms-cppoperkey.cpp b/clang/test/Headers/ms-cppoperkey.cpp
new file mode 100644
index 000000000000..ca56ee17bcb1
--- /dev/null
+++ b/clang/test/Headers/ms-cppoperkey.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 \
+// RUN:     -fms-compatibility -x c++-cpp-output \
+// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     %s -verify
+// expected-no-diagnostics
+# 1 "t.cpp"
+# 1 "query.h" 1 3
+// MS header <query.h> uses operator keyword as field name.  
+// Compile without syntax errors.
+struct tagRESTRICTION
+  {
+   union _URes 
+     {
+       int or; // Note use of cpp operator token
+     } res;
+  };
diff --git a/clang/test/Headers/ms-cppoperkey1.cpp b/clang/test/Headers/ms-cppoperkey1.cpp
new file mode 100644
index 000000000000..c03efc9dacde
--- /dev/null
+++ b/clang/test/Headers/ms-cppoperkey1.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 \
+// RUN:     -fms-compatibility -x c++-cpp-output \
+// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     %s -verify
+
+
+# 1 "t.cpp"
+# 1 "query.h" 1 3 4
+// MS header <query.h> uses operator keyword as field name.  
+// Compile without syntax errors.
+struct tagRESTRICTION
+  {
+   union _URes 
+     {
+       int or; // Note use of cpp operator token
+     } res;
+  };
+   ;
+
+int aa ( int x)
+{
+  // In system header code, treat operator keyword as identifier.
+  if ( // expected-note{{to match this '('}}
+    x>1 or x<0) return 1; // expected-error{{expected ')'}}
+  else return 0;  
+}
+
diff --git a/clang/test/Headers/ms-cppoperkey2.cpp b/clang/test/Headers/ms-cppoperkey2.cpp
new file mode 100644
index 000000000000..2afed36b7446
--- /dev/null
+++ b/clang/test/Headers/ms-cppoperkey2.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1  -triple x86_64-pc-win32 -fms-compatibility \
+// RUN:     -ffreestanding -fsyntax-only -Werror  %s -verify
+// RUN: %clang_cc1 \
+// RUN:     -ffreestanding -fsyntax-only -Werror  %s -verify
+// expected-no-diagnostics
+int bb ( int x)
+{
+  // In user code, treat operator keyword as operator keyword.
+  if ( x>1 or x<0) return 1;
+  else return 0;  
+}