diff --git a/src/os.cc b/src/os.cc
index 70a4a04c4d3d3..cfd86e819a73a 100644
--- a/src/os.cc
+++ b/src/os.cc
@@ -183,11 +183,9 @@ void buffered_file::close() {
 
 int buffered_file::descriptor() const {
 #ifdef FMT_HAS_SYSTEM
-  // fileno is a macro on OpenBSD.
-#  ifdef fileno
-#    undef fileno
-#  endif
   int fd = FMT_POSIX_CALL(fileno(file_));
+#elif defined(_WIN32)
+  int fd = _fileno(file_);
 #else
   int fd = fileno(file_);
 #endif