diff --git a/.gitignore b/.gitignore
index aa227f6..da52c70 100644
--- a/.gitignore
+++ b/.gitignore
@@ -62,3 +62,5 @@
 # Visual Studio Code
 /.vscode/
 /_out
+# VSChromium configuration file
+vs-chromium-project.txt
diff --git a/build/gen.py b/build/gen.py
index ce9d768..fa23266 100755
--- a/build/gen.py
+++ b/build/gen.py
@@ -832,6 +832,7 @@
         'src/gn/visual_studio_writer_unittest.cc',
         'src/gn/xcode_object_unittest.cc',
         'src/gn/xml_element_writer_unittest.cc',
+        'src/util/atomic_write_unittest.cc',
         'src/util/test/gn_test.cc',
       ], 'libs': []},
   }
diff --git a/src/gn/commands.cc b/src/gn/commands.cc
index 030f2d5..93365ad 100644
--- a/src/gn/commands.cc
+++ b/src/gn/commands.cc
@@ -520,6 +520,8 @@
         .PrintToStdout();
     return false;
   }
+  // Close build.ninja or else WriteFileAtomically will fail on Windows.
+  build_ninja_file.close();
   if (util::WriteFileAtomically(build_ninja_path, build_commands.data(),
                                 static_cast<int>(build_commands.size())) ==
       -1) {
diff --git a/src/util/atomic_write_unittest.cc b/src/util/atomic_write_unittest.cc
new file mode 100644
index 0000000..c1d3372
--- /dev/null
+++ b/src/util/atomic_write_unittest.cc
@@ -0,0 +1,36 @@
+// Copyright 2022 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "util/atomic_write.h"
+
+#include <string>
+
+#include "base/files/file_util.h"
+#include "base/files/scoped_temp_dir.h"
+#include "util/test/test.h"
+
+class ImportantFileWriterTest : public testing::Test {
+ public:
+  ImportantFileWriterTest() = default;
+  void SetUp() override {
+    ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
+    file_ = temp_dir_.GetPath().AppendASCII("test-file");
+  }
+
+ protected:
+  base::FilePath file_;
+
+ private:
+  base::ScopedTempDir temp_dir_;
+};
+
+// Test that WriteFileAtomically works.
+TEST_F(ImportantFileWriterTest, Basic) {
+  const std::string data = "Test string for writing.";
+  EXPECT_FALSE(base::PathExists(file_));
+  EXPECT_TRUE(util::WriteFileAtomically(file_, data.data(), data.size()));
+  std::string actual;
+  EXPECT_TRUE(ReadFileToString(file_, &actual));
+  EXPECT_EQ(data, actual);
+}