diff --git a/llvm/unittests/Support/TarWriterTest.cpp b/llvm/unittests/Support/TarWriterTest.cpp
index 927c8ed..6007e73 100644
--- a/llvm/unittests/Support/TarWriterTest.cpp
+++ b/llvm/unittests/Support/TarWriterTest.cpp
@@ -11,6 +11,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "gtest/gtest.h"
+#include <vector>
 
 using namespace llvm;
 namespace {
@@ -37,7 +38,7 @@
 
 class TarWriterTest : public ::testing::Test {};
 
-static UstarHeader create(StringRef Base, StringRef Filename) {
+static std::vector<uint8_t> createTar(StringRef Base, StringRef Filename) {
   // Create a temporary file.
   SmallString<128> Path;
   std::error_code EC =
@@ -55,12 +56,25 @@
   ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr = MemoryBuffer::getFile(Path);
   EXPECT_TRUE((bool)MBOrErr);
   std::unique_ptr<MemoryBuffer> MB = std::move(*MBOrErr);
+  std::vector<uint8_t> Buf((const uint8_t *)MB->getBufferStart(),
+                           (const uint8_t *)MB->getBufferEnd());
+
+  // Windows does not allow us to remove a mmap'ed files, so
+  // unmap first and then remove the temporary file.
+  MB = nullptr;
   sys::fs::remove(Path);
-  return *reinterpret_cast<const UstarHeader *>(MB->getBufferStart());
+
+  return Buf;
+}
+
+static UstarHeader createUstar(StringRef Base, StringRef Filename) {
+  std::vector<uint8_t> Buf = createTar(Base, Filename);
+  EXPECT_TRUE(Buf.size() >= sizeof(UstarHeader));
+  return *reinterpret_cast<const UstarHeader *>(Buf.data());
 }
 
 TEST_F(TarWriterTest, Basics) {
-  UstarHeader Hdr = create("base", "file");
+  UstarHeader Hdr = createUstar("base", "file");
   EXPECT_EQ("ustar", StringRef(Hdr.Magic));
   EXPECT_EQ("00", StringRef(Hdr.Version, 2));
   EXPECT_EQ("base/file", StringRef(Hdr.Name));
@@ -68,21 +82,42 @@
 }
 
 TEST_F(TarWriterTest, LongFilename) {
-  UstarHeader Hdr1 = create(
-      "012345678", std::string(99, 'x') + "/" + std::string(44, 'x') + "/foo");
-  EXPECT_EQ("foo", StringRef(Hdr1.Name));
-  EXPECT_EQ("012345678/" + std::string(99, 'x') + "/" + std::string(44, 'x'),
-            StringRef(Hdr1.Prefix));
+  std::string x154(154, 'x');
+  std::string x155(155, 'x');
+  std::string y99(99, 'y');
+  std::string y100(100, 'y');
 
-  UstarHeader Hdr2 = create(
-      "012345678", std::string(99, 'x') + "/" + std::string(45, 'x') + "/foo");
-  EXPECT_EQ("foo", StringRef(Hdr2.Name));
-  EXPECT_EQ("012345678/" + std::string(99, 'x') + "/" + std::string(45, 'x'),
-            StringRef(Hdr2.Prefix));
+  UstarHeader Hdr1 = createUstar("", x154 + "/" + y99);
+  EXPECT_EQ("/" + x154, StringRef(Hdr1.Prefix));
+  EXPECT_EQ(y99, StringRef(Hdr1.Name));
 
-  UstarHeader Hdr3 = create(
-      "012345678", std::string(99, 'x') + "/" + std::string(46, 'x') + "/foo");
-  EXPECT_EQ(std::string(46, 'x') + "/foo", StringRef(Hdr3.Name));
-  EXPECT_EQ("012345678/" + std::string(99, 'x'), StringRef(Hdr3.Prefix));
+  UstarHeader Hdr2 = createUstar("", x155 + "/" + y99);
+  EXPECT_EQ("", StringRef(Hdr2.Prefix));
+  EXPECT_EQ("", StringRef(Hdr2.Name));
+
+  UstarHeader Hdr3 = createUstar("", x154 + "/" + y100);
+  EXPECT_EQ("", StringRef(Hdr3.Prefix));
+  EXPECT_EQ("", StringRef(Hdr3.Name));
+
+  UstarHeader Hdr4 = createUstar("", x155 + "/" + y100);
+  EXPECT_EQ("", StringRef(Hdr4.Prefix));
+  EXPECT_EQ("", StringRef(Hdr4.Name));
+
+  std::string yz = "yyyyyyyyyyyyyyyyyyyy/zzzzzzzzzzzzzzzzzzzz";
+  UstarHeader Hdr5 = createUstar("", x154 + "/" + yz);
+  EXPECT_EQ("/" + x154, StringRef(Hdr5.Prefix));
+  EXPECT_EQ(yz, StringRef(Hdr5.Name));
+}
+
+TEST_F(TarWriterTest, Pax) {
+  std::vector<uint8_t> Buf = createTar("", std::string(200, 'x'));
+  EXPECT_TRUE(Buf.size() >= 1024);
+
+  auto *Hdr = reinterpret_cast<const UstarHeader *>(Buf.data());
+  EXPECT_EQ("", StringRef(Hdr->Prefix));
+  EXPECT_EQ("", StringRef(Hdr->Name));
+
+  StringRef Pax = StringRef((char *)(Buf.data() + 512), 512);
+  EXPECT_TRUE(Pax.startswith("211 path=/" + std::string(200, 'x')));
 }
 }