diff --git a/src/os.cc b/src/os.cc
index 70a4a04c4d3d3..253b8c4d8b4af 100644
--- a/src/os.cc
+++ b/src/os.cc
@@ -183,13 +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_));
+  int fd = FMT_POSIX_CALL(_fileno(file_));
 #else
-  int fd = fileno(file_);
+  int fd = _fileno(file_);
 #endif
   if (fd == -1)
     FMT_THROW(system_error(errno, FMT_STRING("cannot get file descriptor")));