diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -1300,8 +1300,9 @@
                                 llvm::sys::fs::file_type::regular_file,
                                 llvm::sys::fs::perms::all_all)
             : FS->status(FName);
+    std::error_code EC;
     if (!Res || !Res->exists()) {
-      std::error_code EC = Res.getError();
+      EC = Res.getError();
       if (!InConfigFile) {
         // If the specified file does not exist, leave '@file' unexpanded, as
         // libiberty does.
@@ -1317,6 +1318,12 @@
     }
     const llvm::vfs::Status &FileStatus = Res.get();
 
+    if (FileStatus.isDirectory()) {
+      EC = std::make_error_code(std::errc::is_a_directory);
+      return createStringError(EC, Twine("cannot not open file '") + FName +
+                                       "': " + EC.message());
+    }
+
     auto IsEquivalent =
         [FileStatus, this](const ResponseFileRecord &RFile) -> ErrorOr<bool> {
       ErrorOr<llvm::vfs::Status> RHS = FS->status(RFile.File);
diff --git a/llvm/unittests/Support/CommandLineTest.cpp b/llvm/unittests/Support/CommandLineTest.cpp
--- a/llvm/unittests/Support/CommandLineTest.cpp
+++ b/llvm/unittests/Support/CommandLineTest.cpp
@@ -1060,7 +1060,6 @@
   ASSERT_STREQ(Argv[0], "clang");
   ASSERT_STREQ(Argv[1], AFileExp.c_str());
 
-#if !defined(_AIX) && !defined(__MVS__)
   std::string ADirExp = std::string("@") + std::string(ADir.path());
   Argv = {"clang", ADirExp.c_str()};
   Res = cl::ExpandResponseFiles(Saver, cl::TokenizeGNUCommandLine, Argv);
@@ -1068,7 +1067,6 @@
   ASSERT_EQ(2U, Argv.size());
   ASSERT_STREQ(Argv[0], "clang");
   ASSERT_STREQ(Argv[1], ADirExp.c_str());
-#endif
 }
 
 TEST(CommandLineTest, SetDefaultValue) {