diff --git a/ChangeLog b/ChangeLog
index e6b767e544..6d19538110 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,7 @@
-Tue Jun 25 11:39:34 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Tue Jun 25 11:40:08 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* bignum.c (big2ulong): suppress shorten-64-to-32 warning.  BDIGIT can
+	  be bigger than long now.
 
 	* bignum.c (LSHIFTX): remove redundant never-true expression.
 
diff --git a/bignum.c b/bignum.c
index f15cf832c7..5f8c6d62b3 100644
--- a/bignum.c
+++ b/bignum.c
@@ -2422,8 +2422,8 @@ big2ulong(VALUE x, const char *type, int check)
     ds = BDIGITS(x);
     num = 0;
     while (len--) {
-	num = BIGUP(num);
-	num += ds[len];
+	num <<= BITSPERDIG;
+	num += (unsigned long)ds[len]; /* overflow is already checked */
     }
     return num;
 }