diff --git a/include/clang/Lex/HeaderSearchOptions.h b/include/clang/Lex/HeaderSearchOptions.h
index 5288563..006bf43 100644
--- a/include/clang/Lex/HeaderSearchOptions.h
+++ b/include/clang/Lex/HeaderSearchOptions.h
@@ -28,6 +28,8 @@
     IndexHeaderMap, ///< Like Angled, but marks header maps used when
                        ///  building frameworks.
     System,         ///< Like Angled, but marks system directories.
+    ExternCSystem,  ///< Like System, but headers are implicitly wrapped in
+                    ///  extern "C".
     CSystem,        ///< Like System, but only used for C.
     CXXSystem,      ///< Like System, but only used for C++.
     ObjCSystem,     ///< Like System, but only used for ObjC.
@@ -61,11 +63,9 @@
     unsigned ImplicitExternC : 1;
 
     Entry(StringRef path, frontend::IncludeDirGroup group,
-          bool isFramework, bool ignoreSysRoot, bool isInternal,
-          bool implicitExternC)
+          bool isFramework, bool ignoreSysRoot, bool isInternal)
       : Path(path), Group(group), IsFramework(isFramework),
-        IgnoreSysRoot(ignoreSysRoot), IsInternal(isInternal),
-        ImplicitExternC(implicitExternC) {}
+        IgnoreSysRoot(ignoreSysRoot), IsInternal(isInternal) {}
   };
 
   struct SystemHeaderPrefix {
@@ -126,10 +126,9 @@
 
   /// AddPath - Add the \p Path path to the specified \p Group list.
   void AddPath(StringRef Path, frontend::IncludeDirGroup Group,
-               bool IsFramework, bool IgnoreSysRoot,
-               bool IsInternal = false, bool ImplicitExternC = false) {
+               bool IsFramework, bool IgnoreSysRoot, bool IsInternal = false) {
     UserEntries.push_back(Entry(Path, Group, IsFramework,
-                                IgnoreSysRoot, IsInternal, ImplicitExternC));
+                                IgnoreSysRoot, IsInternal));
   }
 
   /// AddSystemHeaderPrefix - Override whether \#include directives naming a
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index b6a83b2..49f89d4 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -885,10 +885,13 @@
   for (arg_iterator I = Args.filtered_begin(OPT_internal_isystem,
                                             OPT_internal_externc_isystem),
                     E = Args.filtered_end();
-       I != E; ++I)
-    Opts.AddPath((*I)->getValue(), frontend::System,
-                 false, /*IgnoreSysRoot=*/true, /*IsInternal=*/true,
-                 (*I)->getOption().matches(OPT_internal_externc_isystem));
+       I != E; ++I) {
+    frontend::IncludeDirGroup Group = frontend::System;
+    if ((*I)->getOption().matches(OPT_internal_externc_isystem))
+      Group = frontend::ExternCSystem;
+    Opts.AddPath((*I)->getValue(), Group, false, /*IgnoreSysRoot=*/true,
+                 /*IsInternal=*/true);
+  }
 
   // Add the path prefixes which are implicitly treated as being system headers.
   for (arg_iterator I = Args.filtered_begin(OPT_isystem_prefix,
diff --git a/lib/Frontend/InitHeaderSearch.cpp b/lib/Frontend/InitHeaderSearch.cpp
index ba3abba..16b5dd2 100644
--- a/lib/Frontend/InitHeaderSearch.cpp
+++ b/lib/Frontend/InitHeaderSearch.cpp
@@ -53,8 +53,8 @@
   }
 
   /// AddPath - Add the specified path to the specified group list.
-  void AddPath(const Twine &Path, IncludeDirGroup Group,
-               bool isCXXAware, bool isFramework, bool IgnoreSysRoot = false);
+  void AddPath(const Twine &Path, IncludeDirGroup Group, bool isFramework,
+               bool IgnoreSysRoot = false);
 
   /// AddSystemHeaderPrefix - Add the specified prefix to the system header
   /// prefix list.
@@ -111,8 +111,7 @@
 #endif
 }
 
-void InitHeaderSearch::AddPath(const Twine &Path,
-                               IncludeDirGroup Group, bool isCXXAware,
+void InitHeaderSearch::AddPath(const Twine &Path, IncludeDirGroup Group,
                                bool isFramework, bool IgnoreSysRoot) {
   assert(!Path.isTriviallyEmpty() && "can't handle empty path here");
   FileManager &FM = Headers.getFileMgr();
@@ -129,13 +128,13 @@
 
   // Compute the DirectoryLookup type.
   SrcMgr::CharacteristicKind Type;
-  if (Group == Quoted || Group == Angled || Group == IndexHeaderMap)
+  if (Group == Quoted || Group == Angled || Group == IndexHeaderMap) {
     Type = SrcMgr::C_User;
-  else if (isCXXAware)
-    Type = SrcMgr::C_System;
-  else
+  } else if (Group == ExternCSystem) {
     Type = SrcMgr::C_ExternCSystem;
-
+  } else {
+    Type = SrcMgr::C_System;
+  }
 
   // If the directory exists, add it.
   if (const DirectoryEntry *DE = FM.getDirectory(MappedPathStr)) {
@@ -169,42 +168,42 @@
                                                    StringRef Dir64,
                                                    const llvm::Triple &triple) {
   // Add the base dir
-  AddPath(Base, CXXSystem, true, false);
+  AddPath(Base, CXXSystem, false);
 
   // Add the multilib dirs
   llvm::Triple::ArchType arch = triple.getArch();
   bool is64bit = arch == llvm::Triple::ppc64 || arch == llvm::Triple::x86_64;
   if (is64bit)
-    AddPath(Base + "/" + ArchDir + "/" + Dir64, CXXSystem, true, false);
+    AddPath(Base + "/" + ArchDir + "/" + Dir64, CXXSystem, false);
   else
-    AddPath(Base + "/" + ArchDir + "/" + Dir32, CXXSystem, true, false);
+    AddPath(Base + "/" + ArchDir + "/" + Dir32, CXXSystem, false);
 
   // Add the backward dir
-  AddPath(Base + "/backward", CXXSystem, true, false);
+  AddPath(Base + "/backward", CXXSystem, false);
 }
 
 void InitHeaderSearch::AddMinGWCPlusPlusIncludePaths(StringRef Base,
                                                      StringRef Arch,
                                                      StringRef Version) {
   AddPath(Base + "/" + Arch + "/" + Version + "/include/c++",
-          CXXSystem, true, false);
+          CXXSystem, false);
   AddPath(Base + "/" + Arch + "/" + Version + "/include/c++/" + Arch,
-          CXXSystem, true, false);
+          CXXSystem, false);
   AddPath(Base + "/" + Arch + "/" + Version + "/include/c++/backward",
-          CXXSystem, true, false);
+          CXXSystem, false);
 }
 
 void InitHeaderSearch::AddMinGW64CXXPaths(StringRef Base,
                                           StringRef Version) {
   // Assumes Base is HeaderSearchOpts' ResourceDir
   AddPath(Base + "/../../../include/c++/" + Version,
-          CXXSystem, true, false);
+          CXXSystem, false);
   AddPath(Base + "/../../../include/c++/" + Version + "/x86_64-w64-mingw32",
-          CXXSystem, true, false);
+          CXXSystem, false);
   AddPath(Base + "/../../../include/c++/" + Version + "/i686-w64-mingw32",
-          CXXSystem, true, false);
+          CXXSystem, false);
   AddPath(Base + "/../../../include/c++/" + Version + "/backward",
-          CXXSystem, true, false);
+          CXXSystem, false);
 }
 
 void InitHeaderSearch::AddDefaultCIncludePaths(const llvm::Triple &triple,
@@ -220,7 +219,7 @@
       break;
     default:
       // FIXME: temporary hack: hard-coded paths.
-      AddPath("/usr/local/include", System, true, false);
+      AddPath("/usr/local/include", System, false);
       break;
     }
   }
@@ -232,7 +231,7 @@
     // supplied path.
     llvm::sys::Path P(HSOpts.ResourceDir);
     P.appendComponent("include");
-    AddPath(P.str(), System, false, false, /*IgnoreSysRoot=*/ true);
+    AddPath(P.str(), ExternCSystem, false, /*IgnoreSysRoot=*/true);
   }
 
   // All remaining additions are for system include directories, early exit if
@@ -248,7 +247,7 @@
     for (SmallVectorImpl<StringRef>::iterator i = dirs.begin();
          i != dirs.end();
          ++i)
-      AddPath(*i, System, false, false);
+      AddPath(*i, ExternCSystem, false);
     return;
   }
 
@@ -258,62 +257,59 @@
     llvm_unreachable("Include management is handled in the driver.");
 
   case llvm::Triple::Haiku:
-    AddPath("/boot/common/include", System, true, false);
-    AddPath("/boot/develop/headers/os", System, true, false);
-    AddPath("/boot/develop/headers/os/app", System, true, false);
-    AddPath("/boot/develop/headers/os/arch", System, true, false);
-    AddPath("/boot/develop/headers/os/device", System, true, false);
-    AddPath("/boot/develop/headers/os/drivers", System, true, false);
-    AddPath("/boot/develop/headers/os/game", System, true, false);
-    AddPath("/boot/develop/headers/os/interface", System, true, false);
-    AddPath("/boot/develop/headers/os/kernel", System, true, false);
-    AddPath("/boot/develop/headers/os/locale", System, true, false);
-    AddPath("/boot/develop/headers/os/mail", System, true, false);
-    AddPath("/boot/develop/headers/os/media", System, true, false);
-    AddPath("/boot/develop/headers/os/midi", System, true, false);
-    AddPath("/boot/develop/headers/os/midi2", System, true, false);
-    AddPath("/boot/develop/headers/os/net", System, true, false);
-    AddPath("/boot/develop/headers/os/storage", System, true, false);
-    AddPath("/boot/develop/headers/os/support", System, true, false);
-    AddPath("/boot/develop/headers/os/translation", System, true, false);
-    AddPath("/boot/develop/headers/os/add-ons/graphics", System, true, false);
-    AddPath("/boot/develop/headers/os/add-ons/input_server",
-            System, true, false);
-    AddPath("/boot/develop/headers/os/add-ons/screen_saver",
-            System, true, false);
-    AddPath("/boot/develop/headers/os/add-ons/tracker", System, true, false);
-    AddPath("/boot/develop/headers/os/be_apps/Deskbar", System, true, false);
-    AddPath("/boot/develop/headers/os/be_apps/NetPositive",
-            System, true, false);
-    AddPath("/boot/develop/headers/os/be_apps/Tracker", System, true, false);
-    AddPath("/boot/develop/headers/cpp", System, true, false);
-    AddPath("/boot/develop/headers/cpp/i586-pc-haiku", System, true, false);
-    AddPath("/boot/develop/headers/3rdparty", System, true, false);
-    AddPath("/boot/develop/headers/bsd", System, true, false);
-    AddPath("/boot/develop/headers/glibc", System, true, false);
-    AddPath("/boot/develop/headers/posix", System, true, false);
-    AddPath("/boot/develop/headers",  System, true, false);
+    AddPath("/boot/common/include", System, false);
+    AddPath("/boot/develop/headers/os", System, false);
+    AddPath("/boot/develop/headers/os/app", System, false);
+    AddPath("/boot/develop/headers/os/arch", System, false);
+    AddPath("/boot/develop/headers/os/device", System, false);
+    AddPath("/boot/develop/headers/os/drivers", System, false);
+    AddPath("/boot/develop/headers/os/game", System, false);
+    AddPath("/boot/develop/headers/os/interface", System, false);
+    AddPath("/boot/develop/headers/os/kernel", System, false);
+    AddPath("/boot/develop/headers/os/locale", System, false);
+    AddPath("/boot/develop/headers/os/mail", System, false);
+    AddPath("/boot/develop/headers/os/media", System, false);
+    AddPath("/boot/develop/headers/os/midi", System, false);
+    AddPath("/boot/develop/headers/os/midi2", System, false);
+    AddPath("/boot/develop/headers/os/net", System, false);
+    AddPath("/boot/develop/headers/os/storage", System, false);
+    AddPath("/boot/develop/headers/os/support", System, false);
+    AddPath("/boot/develop/headers/os/translation", System, false);
+    AddPath("/boot/develop/headers/os/add-ons/graphics", System, false);
+    AddPath("/boot/develop/headers/os/add-ons/input_server", System, false);
+    AddPath("/boot/develop/headers/os/add-ons/screen_saver", System, false);
+    AddPath("/boot/develop/headers/os/add-ons/tracker", System, false);
+    AddPath("/boot/develop/headers/os/be_apps/Deskbar", System, false);
+    AddPath("/boot/develop/headers/os/be_apps/NetPositive", System, false);
+    AddPath("/boot/develop/headers/os/be_apps/Tracker", System, false);
+    AddPath("/boot/develop/headers/cpp", System, false);
+    AddPath("/boot/develop/headers/cpp/i586-pc-haiku", System, false);
+    AddPath("/boot/develop/headers/3rdparty", System, false);
+    AddPath("/boot/develop/headers/bsd", System, false);
+    AddPath("/boot/develop/headers/glibc", System, false);
+    AddPath("/boot/develop/headers/posix", System, false);
+    AddPath("/boot/develop/headers",  System, false);
     break;
   case llvm::Triple::RTEMS:
     break;
   case llvm::Triple::Cygwin:
-    AddPath("/usr/include/w32api", System, true, false);
+    AddPath("/usr/include/w32api", System, false);
     break;
   case llvm::Triple::MinGW32: { 
       // mingw-w64 crt include paths
       llvm::sys::Path P(HSOpts.ResourceDir);
       P.appendComponent("../../../i686-w64-mingw32/include"); // <sysroot>/i686-w64-mingw32/include
-      AddPath(P.str(), System, true, false);
+      AddPath(P.str(), System, false);
       P = llvm::sys::Path(HSOpts.ResourceDir);
       P.appendComponent("../../../x86_64-w64-mingw32/include"); // <sysroot>/x86_64-w64-mingw32/include
-      AddPath(P.str(), System, true, false);
+      AddPath(P.str(), System, false);
       // mingw.org crt include paths
       P = llvm::sys::Path(HSOpts.ResourceDir);
       P.appendComponent("../../../include"); // <sysroot>/include
-      AddPath(P.str(), System, true, false);
-      AddPath("/mingw/include", System, true, false);
+      AddPath(P.str(), System, false);
+      AddPath("/mingw/include", System, false);
 #if defined(_WIN32)
-      AddPath("c:/mingw/include", System, true, false); 
+      AddPath("c:/mingw/include", System, false); 
 #endif
     }
     break;
@@ -323,7 +319,7 @@
   }
 
   if ( os != llvm::Triple::RTEMS )
-    AddPath("/usr/include", System, false, false);
+    AddPath("/usr/include", ExternCSystem, false);
 }
 
 void InitHeaderSearch::
@@ -400,7 +396,7 @@
 #endif
     break;
   case llvm::Triple::DragonFly:
-    AddPath("/usr/include/c++/4.1", CXXSystem, true, false);
+    AddPath("/usr/include/c++/4.1", CXXSystem, false);
     break;
   case llvm::Triple::FreeBSD:
     // FreeBSD 8.0
@@ -466,15 +462,15 @@
           // Get foo/lib/c++/v1
           P.appendComponent("c++");
           P.appendComponent("v1");
-          AddPath(P.str(), CXXSystem, true, false, true);
+          AddPath(P.str(), CXXSystem, false, true);
         }
       }
       // On Solaris, include the support directory for things like xlocale and
       // fudged system headers.
       if (triple.getOS() == llvm::Triple::Solaris) 
-        AddPath("/usr/include/c++/v1/support/solaris", CXXSystem, true, false);
+        AddPath("/usr/include/c++/v1/support/solaris", CXXSystem, false);
       
-      AddPath("/usr/include/c++/v1", CXXSystem, true, false);
+      AddPath("/usr/include/c++/v1", CXXSystem, false);
     } else {
       AddDefaultCPlusPlusIncludePaths(triple, HSOpts);
     }
@@ -485,8 +481,8 @@
   // Add the default framework include paths on Darwin.
   if (HSOpts.UseStandardSystemIncludes) {
     if (triple.isOSDarwin()) {
-      AddPath("/System/Library/Frameworks", System, true, true);
-      AddPath("/Library/Frameworks", System, true, true);
+      AddPath("/System/Library/Frameworks", System, true);
+      AddPath("/Library/Frameworks", System, true);
     }
   }
 }
@@ -604,7 +600,7 @@
 
   for (path_iterator it = IncludePath.begin(), ie = IncludePath.end();
        it != ie; ++it) {
-    if (it->first == System ||
+    if (it->first == System || it->first == ExternCSystem ||
         (!Lang.ObjC1 && !Lang.CPlusPlus && it->first == CSystem)    ||
         (/*FIXME !Lang.ObjC1 && */Lang.CPlusPlus  && it->first == CXXSystem)  ||
         (Lang.ObjC1  && !Lang.CPlusPlus && it->first == ObjCSystem) ||
@@ -660,8 +656,7 @@
   // Add the user defined entries.
   for (unsigned i = 0, e = HSOpts.UserEntries.size(); i != e; ++i) {
     const HeaderSearchOptions::Entry &E = HSOpts.UserEntries[i];
-    Init.AddPath(E.Path, E.Group, !E.ImplicitExternC, E.IsFramework,
-                 E.IgnoreSysRoot);
+    Init.AddPath(E.Path, E.Group, E.IsFramework, E.IgnoreSysRoot);
   }
 
   Init.AddDefaultIncludePaths(Lang, Triple, HSOpts);
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 8a8f6a2..c07e1e9 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -3692,10 +3692,9 @@
     bool IsFramework = Record[Idx++];
     bool IgnoreSysRoot = Record[Idx++];
     bool IsInternal = Record[Idx++];
-    bool ImplicitExternC = Record[Idx++];
     HSOpts.UserEntries.push_back(
       HeaderSearchOptions::Entry(Path, Group, IsFramework, IgnoreSysRoot,
-                                 IsInternal, ImplicitExternC));
+                                 IsInternal));
   }
 
   // System header prefixes.
diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index d398153..0499f5c 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -1115,7 +1115,6 @@
     Record.push_back(Entry.IsFramework);
     Record.push_back(Entry.IgnoreSysRoot);
     Record.push_back(Entry.IsInternal);
-    Record.push_back(Entry.ImplicitExternC);
   }
 
   // System header prefixes.