diff --git a/llvm/unittests/Support/ReplaceFileTest.cpp b/llvm/unittests/Support/ReplaceFileTest.cpp
index 8b16daf..794f36b 100644
--- a/llvm/unittests/Support/ReplaceFileTest.cpp
+++ b/llvm/unittests/Support/ReplaceFileTest.cpp
@@ -52,6 +52,21 @@
   ~ScopedFD() { Process::SafelyCloseFileDescriptor(FD); }
 };
 
+bool FDHasContent(int FD, StringRef Content) {
+  auto Buffer = MemoryBuffer::getOpenFile(FD, "", -1);
+  assert(Buffer);
+  return Buffer.get()->getBuffer() == Content;
+}
+
+bool FileHasContent(StringRef File, StringRef Content) {
+  int FD = 0;
+  auto EC = fs::openFileForRead(File, FD);
+  (void)EC;
+  assert(!EC);
+  ScopedFD EventuallyCloseIt(FD);
+  return FDHasContent(FD, Content);
+}
+
 TEST(rename, FileOpenedForReadingCanBeReplaced) {
   // Create unique temporary directory for this test.
   SmallString<128> TestDirectory;
@@ -79,25 +94,15 @@
 
     // We should still be able to read the old data through the existing
     // descriptor.
-    auto Buffer = MemoryBuffer::getOpenFile(ReadFD, TargetFileName, -1);
-    ASSERT_TRUE(static_cast<bool>(Buffer));
-    EXPECT_EQ(Buffer.get()->getBuffer(), "!!target!!");
+    EXPECT_TRUE(FDHasContent(ReadFD, "!!target!!"));
 
     // The source file should no longer exist
     EXPECT_FALSE(fs::exists(SourceFileName));
   }
 
-  {
-    // If we obtain a new descriptor for the target file, we should find that it
-    // contains the content that was in the source file.
-    int ReadFD = 0;
-    ASSERT_NO_ERROR(fs::openFileForRead(TargetFileName, ReadFD));
-    ScopedFD EventuallyCloseIt(ReadFD);
-    auto Buffer = MemoryBuffer::getOpenFile(ReadFD, TargetFileName, -1);
-    ASSERT_TRUE(static_cast<bool>(Buffer));
-
-    EXPECT_EQ(Buffer.get()->getBuffer(), "!!source!!");
-  }
+  // If we obtain a new descriptor for the target file, we should find that it
+  // contains the content that was in the source file.
+  EXPECT_TRUE(FileHasContent(TargetFileName, "!!source!!"));
 
   // Rename the target file back to the source file name to confirm that rename
   // still works if the destination does not already exist.
@@ -110,4 +115,59 @@
   ASSERT_NO_ERROR(fs::remove(TestDirectory.str()));
 }
 
+TEST(rename, ExistingTemp) {
+  // Test that existing .tmpN files don't get deleted by the Windows
+  // sys::fs::rename implementation.
+  SmallString<128> TestDirectory;
+  ASSERT_NO_ERROR(
+      fs::createUniqueDirectory("ExistingTemp-test", TestDirectory));
+
+  SmallString<128> SourceFileName(TestDirectory);
+  path::append(SourceFileName, "source");
+
+  SmallString<128> TargetFileName(TestDirectory);
+  path::append(TargetFileName, "target");
+
+  SmallString<128> TargetTmp0FileName(TestDirectory);
+  path::append(TargetTmp0FileName, "target.tmp0");
+
+  SmallString<128> TargetTmp1FileName(TestDirectory);
+  path::append(TargetTmp1FileName, "target.tmp1");
+
+  ASSERT_NO_ERROR(CreateFileWithContent(SourceFileName, "!!source!!"));
+  ASSERT_NO_ERROR(CreateFileWithContent(TargetFileName, "!!target!!"));
+  ASSERT_NO_ERROR(CreateFileWithContent(TargetTmp0FileName, "!!target.tmp0!!"));
+
+  {
+    // Use mapped_file_region to make sure that the destination file is mmap'ed.
+    // This will cause SetInformationByHandle to fail when renaming to the
+    // destination, and we will follow the code path that tries to give target
+    // a temporary name.
+    int TargetFD;
+    std::error_code EC;
+    ASSERT_NO_ERROR(fs::openFileForRead(TargetFileName, TargetFD));
+    ScopedFD X(TargetFD);
+    sys::fs::mapped_file_region MFR(
+        TargetFD, sys::fs::mapped_file_region::readonly, 10, 0, EC);
+    ASSERT_FALSE(EC);
+
+    ASSERT_NO_ERROR(fs::rename(SourceFileName, TargetFileName));
+
+#ifdef _WIN32
+    // Make sure that target was temporarily renamed to target.tmp1 on Windows.
+    // This is signified by a permission denied error as opposed to no such file
+    // or directory when trying to open it.
+    int Tmp1FD;
+    EXPECT_EQ(errc::permission_denied,
+              fs::openFileForRead(TargetTmp1FileName, Tmp1FD));
+#endif
+  }
+
+  EXPECT_TRUE(FileHasContent(TargetTmp0FileName, "!!target.tmp0!!"));
+
+  ASSERT_NO_ERROR(fs::remove(TargetFileName));
+  ASSERT_NO_ERROR(fs::remove(TargetTmp0FileName));
+  ASSERT_NO_ERROR(fs::remove(TestDirectory.str()));
+}
+
 }  // anonymous namespace