diff --git a/file.cpp b/file.cpp
index b1ddc5d..6321fc6 100644
--- a/file.cpp
+++ b/file.cpp
@@ -53,34 +53,47 @@
 
 #ifdef _WIN32
 static int mkstemp(char* name_template, size_t size_in_chars) {
-  auto path = name_template;
-  if (_mktemp_s(path, size_in_chars) != 0) {
+  std::wstring path;
+  CHECK(android::base::UTF8ToWide(name_template, &path))
+      << "path can't be converted to wchar: " << name_template;
+  if (_wmktemp_s(path.data(), path.size() + 1) != 0) {
     return -1;
   }
 
-  std::wstring path_wide;
-  CHECK(android::base::UTF8ToWide(path, &path_wide))
-      << "path can't be converted to wchar: " << path;
-
   // Use open() to match the close() that TemporaryFile's destructor does.
   // Use O_BINARY to match base file APIs.
-  return _wopen(path_wide.c_str(), O_CREAT | O_EXCL | O_RDWR | O_BINARY, S_IRUSR | S_IWUSR);
+  int fd = _wopen(path.c_str(), O_CREAT | O_EXCL | O_RDWR | O_BINARY, S_IRUSR | S_IWUSR);
+  if (fd < 0) {
+    return -1;
+  }
+
+  std::string path_utf8;
+  CHECK(android::base::WideToUTF8(path, &path_utf8)) << "path can't be converted to utf8";
+  CHECK(strcpy_s(name_template, size_in_chars, path_utf8.c_str()) == 0)
+      << "utf8 path can't be assigned back to name_template";
+
+  return fd;
 }
 
 static char* mkdtemp(char* name_template, size_t size_in_chars) {
-  auto path = name_template;
-  if (_mktemp_s(path, size_in_chars) != 0) {
+  std::wstring path;
+  CHECK(android::base::UTF8ToWide(name_template, &path))
+      << "path can't be converted to wchar: " << name_template;
+
+  if (_wmktemp_s(path.data(), path.size() + 1) != 0) {
     return nullptr;
   }
 
-  std::wstring path_wide;
-  CHECK(android::base::UTF8ToWide(path, &path_wide))
-      << "path can't be converted to wchar: " << path;
-
-  if (_wmkdir(path_wide.c_str()) != 0) {
+  if (_wmkdir(path.c_str()) != 0) {
     return nullptr;
   }
-  return path;
+
+  std::string path_utf8;
+  CHECK(android::base::WideToUTF8(path, &path_utf8)) << "path can't be converted to utf8";
+  CHECK(strcpy_s(name_template, size_in_chars, path_utf8.c_str()) == 0)
+      << "utf8 path can't be assigned back to name_template";
+
+  return name_template;
 }
 #endif
 
diff --git a/file_test.cpp b/file_test.cpp
index 65ee235..120228d 100644
--- a/file_test.cpp
+++ b/file_test.cpp
@@ -30,7 +30,7 @@
 #if !defined(_WIN32)
 #include <pwd.h>
 #else
-#include <processenv.h>
+#include <windows.h>
 #endif
 
 #include "android-base/logging.h"  // and must be after windows.h for ERROR
@@ -99,6 +99,11 @@
   std::wstring old_tmp;
   old_tmp.resize(kMaxEnvVariableValueSize);
   old_tmp.resize(GetEnvironmentVariableW(L"TMP", old_tmp.data(), old_tmp.size()));
+  if (old_tmp.empty()) {
+    // Can't continue with empty TMP folder.
+    return;
+  }
+
   std::wstring new_tmp = old_tmp;
   if (new_tmp.back() != L'\\') {
     new_tmp.push_back(L'\\');
@@ -156,14 +161,18 @@
 TEST(file, RootDirectoryWindows) {
   constexpr auto kMaxEnvVariableValueSize = 32767;
   std::wstring old_tmp;
+  bool tmp_is_empty = false;
   old_tmp.resize(kMaxEnvVariableValueSize);
   old_tmp.resize(GetEnvironmentVariableW(L"TMP", old_tmp.data(), old_tmp.size()));
+  if (old_tmp.empty()) {
+    tmp_is_empty = (GetLastError() == ERROR_ENVVAR_NOT_FOUND);
+  }
   SetEnvironmentVariableW(L"TMP", L"C:");
 
   TemporaryFile tf;
   ASSERT_NE(tf.fd, -1) << tf.path;
 
-  SetEnvironmentVariableW(L"TMP", old_tmp.c_str());
+  SetEnvironmentVariableW(L"TMP", tmp_is_empty ? nullptr : old_tmp.c_str());
 }
 #endif