diff --git a/ChangeLog b/ChangeLog
index 84ca5de3c8..a872256f05 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jun 24 23:30:31 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (integer_unpack_single_bdigit): Refine code to filling
+	  higher bits and use BIGLO.
+
 Mon Jun 24 22:26:31 2013  Hiroshi Shirosaki  <h.shirosaki@gmail.com>
 
 	* test/rinda/test_rinda.rb (RingIPv6#prepare_ipv6):
diff --git a/bignum.c b/bignum.c
index 0bdceef045..ffd35cf5e4 100644
--- a/bignum.c
+++ b/bignum.c
@@ -1350,8 +1350,10 @@ integer_unpack_single_bdigit(BDIGIT u, size_t size, int flags, BDIGIT *dp)
         sign = (flags & INTEGER_PACK_NEGATIVE) ?
             ((size == SIZEOF_BDIGITS && u == 0) ? -2 : -1) :
             ((u >> (size * CHAR_BIT - 1)) ? -1 : 1);
-        if (sign < 0)
-            u = (BDIGIT)(-(u | LSHIFTX((~(BDIGIT)0), size * CHAR_BIT)));
+        if (sign < 0) {
+            u |= LSHIFTX(BDIGMAX, size * CHAR_BIT);
+            u = BIGLO(-u);
+        }
     }
     else
         sign = (flags & INTEGER_PACK_NEGATIVE) ? -1 : 1;