diff --git a/ChangeLog b/ChangeLog
index 2dba9ea93d..2675c23605 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Thu Nov 13 12:11:18 2014  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* rb_w32_fstat{,i64}: speed up.  adjuting timestamps in this function
+	  is to get rid of the side effect of ENV["TZ"].  then, if ENV["TZ"] is
+	  not set, no need to adjust.  this change makes File#stat about 60%
+	  faster.
+
 Thu Nov 13 11:56:12 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* st.c: include "internal.h" for STATIC_ASSERT.
diff --git a/win32/win32.c b/win32/win32.c
index 29f95c9a1f..325954ec3e 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -4815,6 +4815,8 @@ rb_w32_fstat(int fd, struct stat *st)
     if (ret) return ret;
 #ifdef __BORLANDC__
     st->st_mode &= ~(S_IWGRP | S_IWOTH);
+#else
+    if (GetEnvironmentVariableW(L"TZ", NULL, 0) == 0 && GetLastError() == ERROR_ENVVAR_NOT_FOUND) return ret;
 #endif
     if (GetFileInformationByHandle((HANDLE)_get_osfhandle(fd), &info)) {
 #ifdef __BORLANDC__
@@ -4835,7 +4837,12 @@ rb_w32_fstati64(int fd, struct stati64 *st)
 {
     BY_HANDLE_FILE_INFORMATION info;
     struct stat tmp;
-    int ret = fstat(fd, &tmp);
+    int ret;
+
+#ifndef __BORLANDC__
+    if (GetEnvironmentVariableW(L"TZ", NULL, 0) == 0 && GetLastError() == ERROR_ENVVAR_NOT_FOUND) return _fstati64(fd, st);
+#endif
+    ret = fstat(fd, &tmp);
 
     if (ret) return ret;
 #ifdef __BORLANDC__