diff --git a/src/if_python3.c b/src/if_python3.c
index 4bbbdd1..8b4bee9 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -34,7 +34,7 @@
 
 #include <limits.h>
 
-#if defined(_WIN32) && defined(HAVE_FCNTL_H)
+#if defined(MSWIN) && defined(HAVE_FCNTL_H)
 # undef HAVE_FCNTL_H
 #endif
 
@@ -112,7 +112,7 @@
 
 #if defined(DYNAMIC_PYTHON3) || defined(PROTO)
 
-# ifndef WIN3264
+# ifndef MSWIN
 #  include <dlfcn.h>
 #  define FARPROC void*
 #  define HINSTANCE void*