diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -18,7 +18,9 @@
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/Path.h"
@@ -2039,6 +2041,30 @@
 
 } // namespace
 
+static const std::string guessSDKPath(const llvm::Triple::OSType OSType) {
+  std::string Platform;
+
+  if (OSType == llvm::Triple::OSType::MacOSX || OSType == llvm::Triple::OSType::Darwin) {
+    // Assume macOS when nothing specific is specified.
+    Platform = "MacOSX";
+  } else if (OSType == llvm::Triple::OSType::IOS) {
+    Platform = "IPhoneOS";
+  } else if (OSType == llvm::Triple::OSType::TvOS) {
+    Platform = "AppleTVOS";
+  } else if (OSType == llvm::Triple::OSType::WatchOS) {
+    Platform = "WatchOS";
+  }
+
+  std::string GuessPath = (
+    "/Applications/Xcode.app/Contents/Developer/Platforms/"
+    + Platform
+    + ".platform/Developer/SDKs/"
+    + Platform
+    + ".sdk");
+
+  return GuessPath;
+}
+
 void Darwin::AddDeploymentTarget(DerivedArgList &Args) const {
   const OptTable &Opts = getDriver().getOpts();
 
@@ -2058,6 +2084,14 @@
         Args.append(Args.MakeSeparateArg(
             nullptr, Opts.getOption(options::OPT_isysroot), env));
       }
+    } else {
+      // If the user doesn't pass -isysroot nor SDKROOT we will try to guess
+      // the standard path of the SDK (in /Applications/Xcode.app ...)
+      const std::string GuessPath = guessSDKPath(getTriple().getOS());
+      if (getVFS().exists(GuessPath)) {
+        Args.append(Args.MakeSeparateArg(
+          nullptr, Opts.getOption(options::OPT_isysroot), GuessPath));
+      }
     }
   }
 
@@ -2251,6 +2285,7 @@
     return DriverArgs.getLastArgValue(options::OPT_isysroot);
   if (!getDriver().SysRoot.empty())
     return getDriver().SysRoot;
+
   return "/";
 }