diff --git a/ChangeLog b/ChangeLog
index 176d71a210..6218232921 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon Apr 16 16:08:18 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* configure.in (RUBY_MSVCRT_VERSION): define on mingw too.
+
+	* win32/Makefile.sub (config.h): prefix RT_VER with RUBY and make
+	  more descriptive to get rid of potential conflict.
+
 Mon Apr 16 15:19:39 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* configure.in (NO_RUBY_VENDOR_LIB): fix missing comma.
diff --git a/configure.in b/configure.in
index c4692742e0..f7e6f3cd95 100644
--- a/configure.in
+++ b/configure.in
@@ -343,6 +343,9 @@ AS_CASE(["$target_os"],
 				   sed -n '/^[[ 	]]*dll name: \(msvc.*\)\.dll$/{s//\1/p;q;}'`],
 		    [rb_cv_msvcrt=msvcrt])
 	test "$rb_cv_msvcrt" = "" && rb_cv_msvcrt=msvcrt])
+	RT_VER=`echo "$rb_cv_msvcrt" | tr -cd [0-9]`
+	test "$RT_VER" = "" && RT_VER=60
+	AC_DEFINE_UNQUOTED(RUBY_MSVCRT_VERSION, $RT_VER)
     ])
     : ${enable_shared=yes}
     ],
diff --git a/error.c b/error.c
index 10061b46a8..bda0f34539 100644
--- a/error.c
+++ b/error.c
@@ -288,7 +288,7 @@ rb_bug(const char *fmt, ...)
     report_bug(file, line, fmt, args);
     va_end(args);
 
-#if defined(_WIN32) && defined(RT_VER) && RT_VER >= 80
+#if defined(_WIN32) && defined(RUBY_MSVCRT_VERSION) && RUBY_MSVCRT_VERSION >= 80
     _set_abort_behavior( 0, _CALL_REPORTFAULT);
 #endif
 
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 0bfd05e857..33ea9835d1 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -474,7 +474,7 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 !if "$(ENABLE_WIN95)" == "yes" && "$(MACHINE)" == "x86"
 #define WIN95 1
 !endif
-#define RT_VER $(RT_VER)
+#define RUBY_MSVCRT_VERSION $(RT_VER)
 #define STDC_HEADERS 1
 #define HAVE_SYS_TYPES_H 1
 #define HAVE_SYS_STAT_H 1
diff --git a/win32/win32.c b/win32/win32.c
index 84c929d371..c114aa7660 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -598,7 +598,7 @@ init_func(void)
 
 static void init_stdhandle(void);
 
-#if RT_VER >= 80
+#if RUBY_MSVCRT_VERSION >= 80
 /* License: Ruby's */
 static void
 invalid_parameter(const wchar_t *expr, const wchar_t *func, const wchar_t *file, unsigned int line, uintptr_t dummy)
@@ -732,7 +732,7 @@ socklist_delete(SOCKET *sockp, int *flagp)
 void
 rb_w32_sysinit(int *argc, char ***argv)
 {
-#if RT_VER >= 80
+#if RUBY_MSVCRT_VERSION >= 80
     static void set_pioinfo_extra(void);
 
     _CrtSetReportMode(_CRT_ASSERT, 0);
@@ -2132,7 +2132,7 @@ typedef struct	{
     int lockinitflag;
     CRITICAL_SECTION lock;
 #endif
-#if RT_VER >= 80
+#if RUBY_MSVCRT_VERSION >= 80
     char textmode;
     char pipech2[2];
 #endif
@@ -2153,7 +2153,7 @@ static inline ioinfo* _pioinfo(int);
 #define _osfile(i)  (_pioinfo(i)->osfile)
 #define _pipech(i)  (_pioinfo(i)->pipech)
 
-#if RT_VER >= 80
+#if RUBY_MSVCRT_VERSION >= 80
 static size_t pioinfo_extra = 0;	/* workaround for VC++8 SP1 */
 
 /* License: Ruby's */
@@ -6208,7 +6208,7 @@ rb_w32_fsopen(const char *path, const char *mode, int shflags)
 }
 #endif
 
-#if defined(_MSC_VER) && RT_VER <= 60
+#if defined(_MSC_VER) && RUBY_MSVCRT_VERSION <= 60
 extern long _ftol(double);
 /* License: Ruby's */
 long