diff --git a/ChangeLog b/ChangeLog
index d97073349e..3df9a35bf9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Mon Jan 31 04:45:12 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* array.c (rb_ary_uniq_bang): call ARY_SET_LEN(ary, 0) before
+	  rb_resize_capa because rb_resize_capa expects resized length is
+	  smaller than current array length. call rb_ary_unshare before
+	  rb_resize_capa because rb_resize_capa losts the reference to
+	  original shared array.
+
 Sun Jan 30 17:19:46 2011  Tanaka Akira  <akr@fsij.org>
 
 	* missing/crypt.c: parenthesize macro arguments.
diff --git a/array.c b/array.c
index 6420e5b645..e776ebdc6a 100644
--- a/array.c
+++ b/array.c
@@ -3484,8 +3484,11 @@ rb_ary_uniq_bang(VALUE ary)
 	if (RARRAY_LEN(ary) == (i = RHASH_SIZE(hash))) {
 	    return Qnil;
 	}
-	ary_resize_capa(ary, i);
 	ARY_SET_LEN(ary, 0);
+	if (ARY_SHARED_P(ary) && !ARY_EMBED_P(ary)) {
+	    rb_ary_unshare(ary);
+	}
+	ary_resize_capa(ary, i);
 	st_foreach(RHASH_TBL(hash), push_value, ary);
     }
     else {