* string.c (rb_str_dup_frozen): handle tail shared string.

git-svn-id: http://svn.ruby-lang.org/repos/ruby/trunk@3165 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 5 insertions, 2 deletions

diff --git a/string.c b/string.c
index 01316b9c2..26d1cbf2a 100644
--- a/string.c
+++ b/string.c
@@ -517,8 +517,11 @@ rb_str_dup_frozen(str)
     VALUE str;
 {
     if (FL_TEST(str, ELTS_SHARED)) {
-	OBJ_FREEZE(RSTRING(str)->aux.shared);
-	return RSTRING(str)->aux.shared;
+	VALUE shared = RSTRING(str)->aux.shared;
+	if (RSTRING(shared)->len == RSTRING(str)->len) {
+	    OBJ_FREEZE(shared);
+	    return shared;
+	}
     }
     if (OBJ_FROZEN(str)) return str;
     str = rb_str_dup(str);