diff --git a/ChangeLog b/ChangeLog
index c137bc431d..5307edb7c3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Nov 16 10:26:41 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* bignum.c (rb_big2ull): add a cast to get rid of a VC++ warning.
+
 Wed Nov 16 09:39:27 2011  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* lib/minitest/unit.rb (assert_raises): experimental fix to run
diff --git a/bignum.c b/bignum.c
index 7f47cf6efb..a1c4ac78a0 100644
--- a/bignum.c
+++ b/bignum.c
@@ -1258,7 +1258,7 @@ rb_big2ull(VALUE x)
     unsigned LONG_LONG num = big2ull(x, "unsigned long long");
 
     if (!RBIGNUM_SIGN(x)) {
-	LONG_LONG v = -num;
+	LONG_LONG v = -(LONG_LONG)num;
 
 	/* FIXNUM_MIN-1 .. LLONG_MIN mapped into 0xbfffffffffffffff .. LONG_MAX+1 */
 	if ((unsigned LONG_LONG)v <= LLONG_MAX)