diff --git a/ChangeLog b/ChangeLog
index 3e20edca7e..e643a13374 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Tue Aug  6 17:42:21 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* win32/win32.c (rb_w32_conv_from_wchar): converted string to CP_UTF8
+	  should have UTF-8 encoding.  otherwise no conversion takes place
+	  later.
+
 Tue Aug  6 17:21:38 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* vm_insnhelper.c (vm_push_frame): fix stack overflow check codes.
diff --git a/win32/win32.c b/win32/win32.c
index 214713697b..fda9e36af7 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -2053,7 +2053,7 @@ rb_w32_conv_from_wchar(const WCHAR *wstr, rb_encoding *enc)
 #endif
 	int clen = rb_long2int(len);
 	len = WideCharToMultiByte(CP_UTF8, 0, wstr, clen, NULL, 0, NULL, NULL);
-	src = rb_enc_str_new(0, len, enc);
+	src = rb_enc_str_new(0, len, rb_enc_from_index(ENCINDEX_UTF_8));
 	WideCharToMultiByte(CP_UTF8, 0, wstr, clen, RSTRING_PTR(src), len, NULL, NULL);
     }
     switch (encindex) {