diff --git a/ChangeLog b/ChangeLog
index 49c8c6ec68..30a3092a0b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Dec 30 16:44:14 2002  Nobuyoshi Nakada  <nobu.nokada@softhome.net>
+
+	* string.c (rb_str_substr): should share the shared string if
+	  present, instead of the original string.  (ruby-bugs:PR#528)
+
 Mon Dec 30 05:10:00 2002  Nobuyoshi Nakada  <nobu.nokada@softhome.net>
 
 	* ext/socket/socket.c (tcp_svr_init): local host to
diff --git a/string.c b/string.c
index d1cbd09cc4..b551afe72d 100644
--- a/string.c
+++ b/string.c
@@ -500,9 +500,12 @@ rb_str_substr(str, beg, len)
     if (len > sizeof(struct RString)/2 &&
 	beg + len == RSTRING(str)->len &&
 	!FL_TEST(str, STR_ASSOC)) {
-	if (!FL_TEST(str, ELTS_SHARED)) str = str_new4(CLASS_OF(str), str);
+	if (FL_TEST(str, ELTS_SHARED))
+	    str = RSTRING(str)->aux.shared;
+	else
+	    str = str_new4(CLASS_OF(str), str);
 	str2 = rb_str_new3(str);
-	RSTRING(str2)->ptr += beg;
+	RSTRING(str2)->ptr += RSTRING(str2)->len - len;
 	RSTRING(str2)->len = len;
     }
     else {