diff --git a/src/os.cc b/src/os.cc
index c682625a..04b4dc50 100644
--- a/src/os.cc
+++ b/src/os.cc
@@ -26,9 +26,6 @@
 #    endif
 #    include <io.h>
 
-#    define O_CREAT _O_CREAT
-#    define O_TRUNC _O_TRUNC
-
 #    ifndef S_IRUSR
 #      define S_IRUSR _S_IREAD
 #    endif
@@ -41,10 +38,6 @@
 #    ifndef S_IROTH
 #      define S_IROTH 0
 #    endif
-
-#    ifdef __MINGW32__
-#      define _SH_DENYNO 0x40
-#    endif
 #  endif  // _WIN32
 #endif    // FMT_USE_FCNTL
 
@@ -107,8 +100,6 @@ int detail::utf16_to_utf8::convert(basic_string_view<wchar_t> s) {
 
 namespace detail {
 
-using mode_t = int;
-
 class system_message {
   system_message(const system_message&) = delete;
   void operator=(const system_message&) = delete;
@@ -220,7 +211,9 @@ int buffered_file::fileno() const {
 
 #if FMT_USE_FCNTL
 file::file(cstring_view path, int oflag) {
-  using namespace detail;
+#  ifdef _WIN32
+  using mode_t = int;
+#  endif
   mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
 #  if defined(_WIN32) && !defined(__MINGW32__)
   fd_ = -1;