Index: lib/Driver/ToolChains/RISCV.h
===================================================================
--- lib/Driver/ToolChains/RISCV.h
+++ lib/Driver/ToolChains/RISCV.h
@@ -23,6 +23,9 @@
                  const llvm::opt::ArgList &Args);
 
   bool IsIntegratedAssemblerDefault() const override { return true; }
+  void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
+                             llvm::opt::ArgStringList &CC1Args,
+                             Action::OffloadKind) const override;
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
@@ -32,6 +35,9 @@
 
 protected:
   Tool *buildLinker() const override;
+
+private:
+  std::string computeSysRoot() const;
 };
 
 } // end namespace toolchains
Index: lib/Driver/ToolChains/RISCV.cpp
===================================================================
--- lib/Driver/ToolChains/RISCV.cpp
+++ lib/Driver/ToolChains/RISCV.cpp
@@ -13,6 +13,7 @@
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Options.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -27,7 +28,7 @@
                                const ArgList &Args)
     : Generic_ELF(D, Triple, Args) {
   GCCInstallation.init(Triple, Args);
-  getFilePaths().push_back(D.SysRoot + "/lib");
+  getFilePaths().push_back(computeSysRoot() + "/lib");
   if (GCCInstallation.isValid()) {
     getFilePaths().push_back(GCCInstallation.getInstallPath().str());
     getProgramPaths().push_back(
@@ -39,13 +40,20 @@
   return new tools::RISCV::Linker(*this);
 }
 
+void RISCVToolChain::addClangTargetOptions(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args,
+    Action::OffloadKind) const {
+  CC1Args.push_back("-nostdsysteminc");
+}
+
 void RISCVToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                                ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdinc))
     return;
 
   if (!DriverArgs.hasArg(options::OPT_nostdlibinc)) {
-    SmallString<128> Dir(getDriver().SysRoot);
+    SmallString<128> Dir(computeSysRoot());
     llvm::sys::path::append(Dir, "include");
     addSystemInclude(DriverArgs, CC1Args, Dir.str());
   }
@@ -54,15 +62,30 @@
 void RISCVToolChain::addLibStdCxxIncludePaths(
     const llvm::opt::ArgList &DriverArgs,
     llvm::opt::ArgStringList &CC1Args) const {
-  StringRef LibDir = GCCInstallation.getParentLibPath();
   const GCCVersion &Version = GCCInstallation.getVersion();
   StringRef TripleStr = GCCInstallation.getTriple().str();
   const Multilib &Multilib = GCCInstallation.getMultilib();
-  addLibStdCXXIncludePaths(
-      LibDir.str() + "/../" + TripleStr.str() + "/include/c++/" + Version.Text,
+  addLibStdCXXIncludePaths(computeSysRoot() + "/include/c++/" + Version.Text,
       "", TripleStr, "", "", Multilib.includeSuffix(), DriverArgs, CC1Args);
 }
 
+std::string RISCVToolChain::computeSysRoot() const {
+  if (!getDriver().SysRoot.empty())
+    return getDriver().SysRoot;
+
+  if (!GCCInstallation.isValid())
+    return std::string();
+
+  StringRef LibDir = GCCInstallation.getParentLibPath();
+  StringRef TripleStr = GCCInstallation.getTriple().str();
+  std::string SysRootDir = LibDir.str() + "/../" + TripleStr.str();
+
+  if (!llvm::sys::fs::exists(SysRootDir))
+    return std::string();
+
+  return SysRootDir;
+}
+
 void RISCV::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                  const InputInfo &Output,
                                  const InputInfoList &Inputs,
Index: test/Driver/riscv32-toolchain.c
===================================================================
--- test/Driver/riscv32-toolchain.c
+++ test/Driver/riscv32-toolchain.c
@@ -24,7 +24,7 @@
 // RUN:   --sysroot=%S/Inputs/basic_riscv32_tree/riscv32-unknown-elf 2>&1 \
 // RUN:   | FileCheck -check-prefix=CXX-RV32-BAREMETAL-ILP32 %s
 
-// CXX-RV32-BAREMETAL-ILP32: "-internal-isystem" "{{.*}}Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../../../riscv32-unknown-elf/include/c++{{/|\\\\}}8.0.1"
+// CXX-RV32-BAREMETAL-ILP32: "-internal-isystem" "{{.*}}Inputs/basic_riscv32_tree/riscv32-unknown-elf/include/c++{{/|\\\\}}8.0.1"
 // CXX-RV32-BAREMETAL-ILP32: "{{.*}}Inputs/basic_riscv32_tree/lib/gcc/riscv32-unknown-elf/8.0.1/../../../../bin{{/|\\\\}}riscv32-unknown-elf-ld"
 // CXX-RV32-BAREMETAL-ILP32: "--sysroot={{.*}}/Inputs/basic_riscv32_tree/riscv32-unknown-elf"
 // CXX-RV32-BAREMETAL-ILP32: "{{.*}}/Inputs/basic_riscv32_tree/riscv32-unknown-elf/lib{{/|\\\\}}crt0.o"