diff --git a/ChangeLog b/ChangeLog
index 23c8174af2..27c746c766 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Dec 15 18:24:21 2012  Tadayoshi Funaba  <tadf@dotrb.org>
+
+	* rational.c (f_round_common): should check overflow.
+
 Sat Dec 15 18:00:00 2012  Tadayoshi Funaba  <tadf@dotrb.org>
 
 	* ratioanl.c (float_rationalize): reduced.
diff --git a/rational.c b/rational.c
index c8d5688c94..afa4bd4cec 100644
--- a/rational.c
+++ b/rational.c
@@ -1210,6 +1210,12 @@ f_round_common(int argc, VALUE *argv, VALUE self, VALUE (*func)(VALUE))
     b = f_expt10(n);
     s = f_mul(self, b);
 
+    if (k_float_p(s)) {
+	if (f_lt_p(n, ZERO))
+	    return ZERO;
+	return self;
+    }
+
     s = (*func)(s);
 
     s = f_div(f_rational_new_bang1(CLASS_OF(self), s), b);