diff --git a/ChangeLog b/ChangeLog
index 5e23371453..9d81e2d109 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Mon May  2 23:03:42 2016  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* win32/win32.c, include/ruby/win32.h (rb_w32_utruncate): implements new
+	  truncate alternative which accepts UTF-8 path.
+
+	* file.c (truncate): use above function.
+	  [Bug #12340]
+
 Mon May  2 20:59:21 2016  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* re.c (str_coderange): to avoid function call when the string already
diff --git a/file.c b/file.c
index 0b469992d3..fab1b343c1 100644
--- a/file.c
+++ b/file.c
@@ -100,6 +100,8 @@ int flock(int, int);
 #define lstat(p, s)	rb_w32_ulstati64((p), (s))
 #undef access
 #define access(p, m)	rb_w32_uaccess((p), (m))
+#undef truncate
+#define truncate(p, n)	rb_w32_utruncate((p), (n))
 #undef chmod
 #define chmod(p, m)	rb_w32_uchmod((p), (m))
 #undef chown
diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index 47f68b8cb2..68b8db73e6 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -403,8 +403,9 @@ __declspec(dllimport) extern int finite(double);
 
 #define SUFFIX
 
-extern int 	 rb_w32_ftruncate(int fd, off_t length);
-extern int 	 rb_w32_truncate(const char *path, off_t length);
+extern int rb_w32_ftruncate(int fd, off_t length);
+extern int rb_w32_truncate(const char *path, off_t length);
+extern int rb_w32_utruncate(const char *path, off_t length);
 
 #undef HAVE_FTRUNCATE
 #define HAVE_FTRUNCATE 1
diff --git a/win32/win32.c b/win32/win32.c
index eb32b35d43..8ca3dbf979 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -5702,21 +5702,41 @@ rb_chsize(HANDLE h, off_t size)
 }
 
 /* License: Ruby's */
-int
-rb_w32_truncate(const char *path, off_t length)
+static int
+w32_truncate(const char *path, off_t length, UINT cp)
 {
     HANDLE h;
     int ret;
-    h = CreateFile(path, GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0);
+    WCHAR *wpath;
+
+    if (!(wpath = mbstr_to_wstr(cp, path, -1, NULL)))
+	return -1;
+    h = CreateFileW(wpath, GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0);
     if (h == INVALID_HANDLE_VALUE) {
 	errno = map_errno(GetLastError());
+	free(wpath);
 	return -1;
     }
+    free(wpath);
     ret = rb_chsize(h, length);
     CloseHandle(h);
     return ret;
 }
 
+/* License: Ruby's */
+int
+rb_w32_utruncate(const char *path, off_t length)
+{
+    return w32_truncate(path, length, CP_UTF8);
+}
+
+/* License: Ruby's */
+int
+rb_w32_truncate(const char *path, off_t length)
+{
+    return w32_truncate(path, length, filecp());
+}
+
 /* License: Ruby's */
 int
 rb_w32_ftruncate(int fd, off_t length)