diff --git a/posix.cc b/posix.cc
index d36871f4..756281a0 100644
--- a/posix.cc
+++ b/posix.cc
@@ -55,11 +55,14 @@
 
 # ifdef __MINGW32__
 #  define _SH_DENYNO 0x40
-#  undef fileno
 # endif
 
 #endif  // _WIN32
 
+#ifdef fileno
+# undef fileno
+#endif
+
 namespace {
 #ifdef _WIN32
 // Return type of read and write functions.