diff --git a/ChangeLog b/ChangeLog
index e51ac1f596..a7e00cca44 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -18,6 +18,11 @@ Thu Jun 18 16:21:05 2009  Ryan Davis  <ryand-ruby@zenspider.com>
 	* lib/minitest/*.rb: Imported minitest 1.4.0 r5083.
 	* test/minitest/*.rb: ditto.
 
+Thu Jun 18 10:12:49 2009  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* ext/bigdecimal/bigdecimal.c (BigDecimal_to_f): went infinity too
+	  early.  add BASE_FIG margin.  [ruby-dev:38673]
+
 Thu Jun 18 01:35:51 2009  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* numeric.c (flo_cmp): Infinity is greater than any bignum
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index d80e0a764e..0b2ac34b15 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -605,7 +605,7 @@ BigDecimal_to_f(VALUE self)
 
     GUARD_OBJ(p,GetVpValue(self,1));
     if (VpVtoD(&d, &e, p)!=1) return rb_float_new(d);
-    if (e > DBL_MAX_10_EXP) goto erange;
+    if (e > DBL_MAX_10_EXP+BASE_FIG) goto erange;
     str = rb_str_new(0, VpNumOfChars(p,"E"));
     buf = RSTRING_PTR(str);
     VpToString(p, buf, 0, 0);