diff --git a/ChangeLog b/ChangeLog
index bac9758b39..00bad3641b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Feb 11 15:47:10 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* array.c (ary_make_shared): returns shared root array itself, and
+	  frozen array can be shared.
+
 Wed Feb 11 14:46:16 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* insns.def (setspecial, putstring): fixed typos in rdoc.
diff --git a/array.c b/array.c
index c35e113851..35023f3209 100644
--- a/array.c
+++ b/array.c
@@ -211,14 +211,16 @@ rb_ary_unshare(VALUE ary)
 }
 
 static inline void
-rb_ary_unshare_safe(VALUE ary) {
+rb_ary_unshare_safe(VALUE ary)
+{
     if (ARY_SHARED_P(ary) && !ARY_EMBED_P(ary)) {
 	rb_ary_unshare(ary);
     }
 }
 
 static VALUE
-rb_ary_increment_share(VALUE shared) {
+rb_ary_increment_share(VALUE shared)
+{
     int num = ARY_SHARED_NUM(shared);
     if (num >= 0) {
 	ARY_SET_SHARED_NUM(shared, num + 1);
@@ -390,6 +392,15 @@ ary_make_shared(VALUE ary)
     if (ARY_SHARED_P(ary)) {
 	return ARY_SHARED(ary);
     }
+    else if (ARY_SHARED_ROOT_P(ary)) {
+	return ary;
+    }
+    else if (OBJ_FROZEN(ary)) {
+	ary_resize_capa(ary, ARY_HEAP_LEN(ary));
+	FL_SET_SHARED_ROOT(ary);
+	ARY_SET_SHARED_NUM(ary, 0);
+	return ary;
+    }
     else {
 	NEWOBJ(shared, struct RArray);
 	OBJSETUP(shared, 0, T_ARRAY);
@@ -2389,7 +2400,8 @@ rb_ary_replace(VALUE copy, VALUE orig)
         VALUE shared = ary_make_shared(orig);
         if (ARY_OWNS_HEAP_P(copy)) {
             xfree(RARRAY_PTR(copy));
-        } else {
+        }
+        else {
             rb_ary_unshare_safe(copy);
         }
         FL_UNSET_EMBED(copy);