diff --git a/src/if_ruby.c b/src/if_ruby.c
index 24814a2..85f94c4 100644
--- a/src/if_ruby.c
+++ b/src/if_ruby.c
@@ -64,7 +64,7 @@
 #  define RUBY_EXPORT
 # endif
 
-#if !(defined(WIN32) || defined(_WIN64))
+#if !defined(MSWIN)
 # include <dlfcn.h>
 # define HINSTANCE void*
 # define RUBY_PROC void*
@@ -331,7 +331,7 @@
 # endif
 # define ruby_init			dll_ruby_init
 # define ruby_init_loadpath		dll_ruby_init_loadpath
-# ifdef WIN3264
+# ifdef MSWIN
 #  ifdef RUBY19_OR_LATER
 #   define ruby_sysinit			dll_ruby_sysinit
 #  else
@@ -447,7 +447,7 @@
 # endif
 static void (*dll_ruby_init) (void);
 static void (*dll_ruby_init_loadpath) (void);
-# ifdef WIN3264
+# ifdef MSWIN
 #  ifdef RUBY19_OR_LATER
 static void (*dll_ruby_sysinit) (int*, char***);
 #  else
@@ -666,7 +666,7 @@
 # endif
     {"ruby_init", (RUBY_PROC*)&dll_ruby_init},
     {"ruby_init_loadpath", (RUBY_PROC*)&dll_ruby_init_loadpath},
-# ifdef WIN3264
+# ifdef MSWIN
 #  ifdef RUBY19_OR_LATER
     {"ruby_sysinit", (RUBY_PROC*)&dll_ruby_sysinit},
 #  else
@@ -949,7 +949,7 @@
 	if (ruby_enabled(TRUE))
 	{
 #endif
-#ifdef _WIN32
+#ifdef MSWIN
 	    /* suggested by Ariya Mizutani */
 	    int argc = 1;
 	    char *argv[] = {"gvim.exe"};