diff --git a/test/os-test.cc b/test/os-test.cc
index 079ec920..7a18a3b4 100644
--- a/test/os-test.cc
+++ b/test/os-test.cc
@@ -10,6 +10,7 @@
 #include <cstdlib>  // std::exit
 #include <cstring>
 #include <memory>
+#include <mutex>
 
 #include "gtest-extra.h"
 #include "util.h"
@@ -17,6 +18,14 @@
 using fmt::buffered_file;
 using testing::HasSubstr;
 using wstring_view = fmt::basic_string_view<wchar_t>;
+std::mutex mutex_file_name;
+std::string get_test_file_name() {
+  static int index = 0;
+  mutex_file_name.lock();
+  std::string test_file = "test-file-" + std::to_string(index++);
+  mutex_file_name.unlock();
+  return test_file;
+}
 
 #ifdef _WIN32
 
@@ -90,10 +99,11 @@ TEST(os_test, report_windows_error) {
 #  if FMT_USE_FCNTL && !defined(__MINGW32__)
 TEST(file_test, open_windows_file) {
   using fmt::file;
-  file out = file::open_windows_file(L"test-file",
+std::string test_file = get_test_file_name();
+	file out = file::open_windows_file(test_file,
                                      file::WRONLY | file::CREATE | file::TRUNC);
   out.write("x", 1);
-  file in = file::open_windows_file(L"test-file", file::RDONLY);
+	file in = file::open_windows_file(test_file, file::RDONLY);
   EXPECT_READ(in, "x");
 }
 #  endif  // FMT_USE_FCNTL && !defined(__MINGW32__)
@@ -232,68 +242,74 @@ TEST(buffered_file_test, descriptor) {
 }
 
 TEST(ostream_test, move) {
-  fmt::ostream out = fmt::output_file("test-file");
+	fmt::ostream out = fmt::output_file(get_test_file_name());
   fmt::ostream moved(std::move(out));
   moved.print("hello");
 }
 
 TEST(ostream_test, move_while_holding_data) {
+std::string test_file = get_test_file_name();
   {
-    fmt::ostream out = fmt::output_file("test-file");
+	fmt::ostream out = fmt::output_file(test_file);
     out.print("Hello, ");
     fmt::ostream moved(std::move(out));
     moved.print("world!\n");
   }
   {
-    file in("test-file", file::RDONLY);
+	file in(test_file, file::RDONLY);
     EXPECT_READ(in, "Hello, world!\n");
   }
 }
 
 TEST(ostream_test, print) {
-  fmt::ostream out = fmt::output_file("test-file");
+std::string test_file = get_test_file_name();
+	fmt::ostream out = fmt::output_file(test_file);
   out.print("The answer is {}.\n", 42);
   out.close();
-  file in("test-file", file::RDONLY);
+	file in(test_file, file::RDONLY);
   EXPECT_READ(in, "The answer is 42.\n");
 }
 
 TEST(ostream_test, buffer_boundary) {
+std::string test_file = get_test_file_name();
   auto str = std::string(4096, 'x');
-  fmt::ostream out = fmt::output_file("test-file");
+	fmt::ostream out = fmt::output_file(test_file);
   out.print("{}", str);
   out.print("{}", str);
   out.close();
-  file in("test-file", file::RDONLY);
+	file in(test_file, file::RDONLY);
   EXPECT_READ(in, str + str);
 }
 
 TEST(ostream_test, buffer_size) {
-  fmt::ostream out = fmt::output_file("test-file", fmt::buffer_size = 1);
+std::string test_file = get_test_file_name();
+	fmt::ostream out = fmt::output_file(test_file, fmt::buffer_size = 1);
   out.print("{}", "foo");
   out.close();
-  file in("test-file", file::RDONLY);
+	file in(test_file, file::RDONLY);
   EXPECT_READ(in, "foo");
 }
 
 TEST(ostream_test, truncate) {
+std::string test_file = get_test_file_name();
   {
-    fmt::ostream out = fmt::output_file("test-file");
+	fmt::ostream out = fmt::output_file(test_file);
     out.print("0123456789");
   }
   {
-    fmt::ostream out = fmt::output_file("test-file");
+	fmt::ostream out = fmt::output_file(test_file);
     out.print("foo");
   }
-  file in("test-file", file::RDONLY);
+	file in(test_file, file::RDONLY);
   EXPECT_EQ("foo", read(in, 4));
 }
 
 TEST(ostream_test, flush) {
-  auto out = fmt::output_file("test-file");
+std::string test_file = get_test_file_name();
+	auto out = fmt::output_file(test_file);
   out.print("x");
   out.flush();
-  auto in = fmt::file("test-file", file::RDONLY);
+	auto in = fmt::file(test_file, file::RDONLY);
   EXPECT_READ(in, "x");
 }
 
@@ -417,7 +433,7 @@ TEST(file_test, read) {
 }
 
 TEST(file_test, read_error) {
-  file f("test-file", file::WRONLY);
+	file f(get_test_file_name(), file::WRONLY);
   char buf;
   // We intentionally read from a file opened in the write-only mode to
   // cause error.
@@ -432,7 +448,7 @@ TEST(file_test, write) {
 }
 
 TEST(file_test, write_error) {
-  file f("test-file", file::RDONLY);
+	file f(get_test_file_name(), file::RDONLY);
   // We intentionally write to a file opened in the read-only mode to
   // cause error.
   EXPECT_SYSTEM_ERROR(f.write(" ", 1), EBADF, "cannot write to file");