--- a/clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ b/clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -174,7 +174,7 @@ WebAssembly::WebAssembly(const Driver &D
 
   getProgramPaths().push_back(getDriver().getInstalledDir());
 
-  auto SysRoot = getDriver().SysRoot;
+  std::string SysRoot = computeSysRoot();
   if (getTriple().getOS() == llvm::Triple::UnknownOS) {
     // Theoretically an "unknown" OS should mean no standard libraries, however
     // it could also mean that a custom set of libraries is in use, so just add
@@ -402,6 +402,7 @@ void WebAssembly::AddClangSystemIncludeA
     return;
 
   const Driver &D = getDriver();
+  std::string SysRoot = computeSysRoot();
 
   if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> P(D.ResourceDir);
@@ -427,10 +428,10 @@ void WebAssembly::AddClangSystemIncludeA
 
   if (getTriple().getOS() != llvm::Triple::UnknownOS) {
     const std::string MultiarchTriple =
-        getMultiarchTriple(D, getTriple(), D.SysRoot);
-    addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include/" + MultiarchTriple);
+        getMultiarchTriple(D, getTriple(), SysRoot);
+    addSystemInclude(DriverArgs, CC1Args, SysRoot + "/include/" + MultiarchTriple);
   }
-  addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include");
+  addSystemInclude(DriverArgs, CC1Args, SysRoot + "/include");
 }
 
 void WebAssembly::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
@@ -478,6 +479,17 @@ Tool *WebAssembly::buildLinker() const {
   return new tools::wasm::Linker(*this);
 }
 
+std::string WebAssembly::computeSysRoot() const {
+  if (!getDriver().SysRoot.empty())
+    return getDriver().SysRoot;
+
+  std::string Path = "/usr";
+  if (getVFS().exists(Path))
+    return Path;
+
+  return std::string();
+}
+
 void WebAssembly::addLibCxxIncludePaths(
     const llvm::opt::ArgList &DriverArgs,
     llvm::opt::ArgStringList &CC1Args) const {
--- a/clang/lib/Driver/ToolChains/WebAssembly.h
+++ b/clang/lib/Driver/ToolChains/WebAssembly.h
@@ -89,6 +89,8 @@ private:
                              llvm::opt::ArgStringList &CC1Args) const;
   void addLibStdCXXIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                 llvm::opt::ArgStringList &CC1Args) const;
+
+  std::string computeSysRoot() const override;
 };
 
 } // end namespace toolchains