diff --git a/ChangeLog b/ChangeLog
index 8e864015b6..1772aa2fbf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Tue Jun 25 20:08:29 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (rb_big2ulong_pack): Use rb_integer_pack.
+	  (rb_big_aref): Call big2ulong with TRUE for "check" argument.
+	  It should be non-effective.
+
 Tue Jun 25 19:07:33 2013  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (LSHIFTX): Revert r41611.
diff --git a/bignum.c b/bignum.c
index f9cd368dee..e9b58ce25a 100644
--- a/bignum.c
+++ b/bignum.c
@@ -2438,10 +2438,9 @@ big2ulong(VALUE x, const char *type, int check)
 VALUE
 rb_big2ulong_pack(VALUE x)
 {
-    unsigned long num = big2ulong(x, "unsigned long", FALSE);
-    if (!RBIGNUM_SIGN(x)) {
-	return (VALUE)(-(SIGNED_VALUE)num);
-    }
+    unsigned long num;
+    rb_integer_pack(x, &num, 1, sizeof(num), 0,
+        INTEGER_PACK_NATIVE_BYTE_ORDER|INTEGER_PACK_2COMP);
     return num;
 }
 
@@ -5068,7 +5067,7 @@ rb_big_aref(VALUE x, VALUE y)
 	  out_of_range:
 	    return RBIGNUM_SIGN(x) ? INT2FIX(0) : INT2FIX(1);
 	}
-	shift = big2ulong(y, "long", FALSE);
+	shift = big2ulong(y, "long", TRUE);
     }
     else {
 	i = NUM2LONG(y);