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.
diff --git a/test/posix-test.cc b/test/posix-test.cc
index 7dd0dbb0..007e2507 100644
--- a/test/posix-test.cc
+++ b/test/posix-test.cc
@@ -31,7 +31,7 @@
 #include "posix.h"
 #include "util.h"
 
-#ifdef __MINGW32__
+#ifdef fileno
 # undef fileno
 #endif