Index: include/clang/Driver/Driver.h
===================================================================
--- include/clang/Driver/Driver.h
+++ include/clang/Driver/Driver.h
@@ -145,6 +145,9 @@
   /// sysroot, if present
   std::string SysRoot;
 
+  /// Include sysroot, if present
+  std::string IncludeSysRoot;
+
   /// Dynamic loader prefix, if present
   std::string DyldPrefix;
 
Index: lib/Driver/Driver.cpp
===================================================================
--- lib/Driver/Driver.cpp
+++ lib/Driver/Driver.cpp
@@ -88,7 +88,8 @@
     : Opts(createDriverOptTable()), Diags(Diags), VFS(std::move(VFS)),
       Mode(GCCMode), SaveTemps(SaveTempsNone), BitcodeEmbed(EmbedNone),
       LTOMode(LTOK_None), ClangExecutable(ClangExecutable),
-      SysRoot(DEFAULT_SYSROOT), UseStdLib(true),
+      SysRoot(DEFAULT_SYSROOT), IncludeSysRoot(DEFAULT_SYSROOT),
+      UseStdLib(true),
       DriverTitle("clang LLVM compiler"), CCPrintOptionsFilename(nullptr),
       CCPrintHeadersFilename(nullptr), CCLogDiagnosticsFilename(nullptr),
       CCCPrintBindings(false), CCPrintHeaders(false), CCLogDiagnostics(false),
@@ -677,6 +678,10 @@
   }
   if (const Arg *A = Args.getLastArg(options::OPT__sysroot_EQ))
     SysRoot = A->getValue();
+  if (const Arg *A = Args.getLastArg(options::OPT_isysroot))
+    IncludeSysRoot = A->getValue();
+  if (IncludeSysRoot.empty() && !SysRoot.empty())
+    IncludeSysRoot = SysRoot;
   if (const Arg *A = Args.getLastArg(options::OPT__dyld_prefix_EQ))
     DyldPrefix = A->getValue();
   if (Args.hasArg(options::OPT_nostdlib))
Index: lib/Driver/ToolChains/Linux.h
===================================================================
--- lib/Driver/ToolChains/Linux.h
+++ lib/Driver/ToolChains/Linux.h
@@ -40,6 +40,7 @@
   void addProfileRTLibs(const llvm::opt::ArgList &Args,
                         llvm::opt::ArgStringList &CmdArgs) const override;
   virtual std::string computeSysRoot() const;
+  virtual std::string computeIncludeSysRoot() const;
 
   virtual std::string getDynamicLinker(const llvm::opt::ArgList &Args) const;
 
@@ -48,6 +49,7 @@
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
+  std::string defaultSysRoot() const;
 };
 
 } // end namespace toolchains
Index: lib/Driver/ToolChains/Linux.cpp
===================================================================
--- lib/Driver/ToolChains/Linux.cpp
+++ lib/Driver/ToolChains/Linux.cpp
@@ -380,10 +380,7 @@
   return new tools::gnutools::Assembler(*this);
 }
 
-std::string Linux::computeSysRoot() const {
-  if (!getDriver().SysRoot.empty())
-    return getDriver().SysRoot;
-
+std::string Linux::defaultSysRoot() const {
   if (!GCCInstallation.isValid() || !tools::isMipsArch(getTriple().getArch()))
     return std::string();
 
@@ -410,6 +407,20 @@
   return std::string();
 }
 
+std::string Linux::computeSysRoot() const {
+  if (!getDriver().SysRoot.empty())
+    return getDriver().SysRoot;
+
+  return defaultSysRoot();
+}
+
+std::string Linux::computeIncludeSysRoot() const {
+  if (!getDriver().IncludeSysRoot.empty())
+    return getDriver().IncludeSysRoot;
+
+  return defaultSysRoot();
+}
+
 std::string Linux::getDynamicLinker(const ArgList &Args) const {
   const llvm::Triple::ArchType Arch = getArch();
   const llvm::Triple &Triple = getTriple();
@@ -541,7 +552,7 @@
 void Linux::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                       ArgStringList &CC1Args) const {
   const Driver &D = getDriver();
-  std::string SysRoot = computeSysRoot();
+  std::string SysRoot = computeIncludeSysRoot();
 
   if (DriverArgs.hasArg(clang::driver::options::OPT_nostdinc))
     return;
@@ -732,8 +743,8 @@
       // If this is a development, non-installed, clang, libcxx will
       // not be found at ../include/c++ but it likely to be found at
       // one of the following two locations:
-      DetectLibcxxIncludePath(getDriver().SysRoot + "/usr/local/include/c++"),
-      DetectLibcxxIncludePath(getDriver().SysRoot + "/usr/include/c++") };
+      DetectLibcxxIncludePath(getDriver().IncludeSysRoot + "/usr/local/include/c++"),
+      DetectLibcxxIncludePath(getDriver().IncludeSysRoot + "/usr/include/c++") };
   for (const auto &IncludePath : LibCXXIncludePathCandidates) {
     if (IncludePath.empty() || !getVFS().exists(IncludePath))
       continue;