Index: flang/test/Driver/response-file.f90
===================================================================
--- /dev/null
+++ flang/test/Driver/response-file.f90
@@ -0,0 +1,15 @@
+! Test that the driver can process response files.
+
+! RUN: echo "-DTEST" > %basename_t.rsp
+! RUN: %flang -E -cpp @%basename_t.rsp %s -o - | FileCheck %s
+! RUN: %flang_fc1 -E -cpp @%basename_t.rsp %s -o - | FileCheck %s
+
+! CHECK-LABEL: program test
+! CHECK: end program
+
+#ifdef TEST
+program test
+end program
+#else
+We should have read the define from the response file.
+#endif
Index: flang/tools/flang-driver/driver.cpp
===================================================================
--- flang/tools/flang-driver/driver.cpp
+++ flang/tools/flang-driver/driver.cpp
@@ -20,6 +20,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/VirtualFileSystem.h"
@@ -75,6 +76,13 @@
   clang::driver::ParsedClangName targetandMode("flang", "--driver-mode=flang");
   std::string driverPath = GetExecutablePath(args[0]);
 
+  // Parse response files. We're defaulting to the GNU syntax, since we don't
+  // have a CL mode.
+  llvm::BumpPtrAllocator a;
+  llvm::StringSaver saver(a);
+  llvm::cl::TokenizerCallback tokenizer = &llvm::cl::TokenizeGNUCommandLine;
+  llvm::cl::ExpandResponseFiles(saver, tokenizer, args, /* MarkEOLs=*/false);
+
   // Check if flang-new is in the frontend mode
   auto firstArg = std::find_if(
       args.begin() + 1, args.end(), [](const char *a) { return a != nullptr; });