diff --git a/clang/tools/driver/driver.cpp b/clang/tools/driver/driver.cpp
--- a/clang/tools/driver/driver.cpp
+++ b/clang/tools/driver/driver.cpp
@@ -385,10 +385,22 @@
   bool MarkEOLs = ClangCLMode;
 
   llvm::cl::TokenizerCallback Tokenizer;
-  if (RSPQuoting == Windows || (RSPQuoting == Default && ClangCLMode))
+  switch (RSPQuoting) {
+  case Default: {
+    if (ClangCLMode ||
+        llvm::Triple(llvm::sys::getProcessTriple()).isOSWindows())
+      Tokenizer = &llvm::cl::TokenizeWindowsCommandLine;
+    else
+      Tokenizer = &llvm::cl::TokenizeGNUCommandLine;
+    break;
+  }
+  case Windows:
     Tokenizer = &llvm::cl::TokenizeWindowsCommandLine;
-  else
+    break;
+  case POSIX:
     Tokenizer = &llvm::cl::TokenizeGNUCommandLine;
+    break;
+  }
 
   if (MarkEOLs && argv.size() > 1 && StringRef(argv[1]).startswith("-cc1"))
     MarkEOLs = false;