diff --git a/ChangeLog b/ChangeLog
index 5118d21127..22938adafd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Dec 21 16:10:30 2007  Shigeo Kobayashi  <shigeo@tinyforest.jp>
+
+	* ext/bigdecimal/bigdecimal.c (VpMidRound): Round method bug
+	  pointed by Ryan Platte fixed(Patch to the patch from "NATORI
+	  Shin").  [ruby-talk:273360]
+
 Fri Dec 21 16:06:13 2007  Tanaka Akira  <akr@fsij.org>
 
 	* re.c (append_utf8): use rb_utf8_encoding() instead of
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index c9e7ceb2e4..d2a351e984 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -4318,7 +4318,6 @@ Exit:
 
 /*
  *
- * f = 0: Round off/Truncate, 1: round up, 2:ceil, 3: floor, 4: Banker's rounding
  * nf: digit position for operation.
  *
  */
@@ -4339,15 +4338,22 @@ VpMidRound(Real *y, int f, int nf)
     nf += y->exponent*((int)BASE_FIG);
     exptoadd=0;
     if (nf < 0) {
+		/* rounding position too left(large). */
+		if((f!=VP_ROUND_CEIL) && (f!=VP_ROUND_FLOOR)) {
+			VpSetZero(y,VpGetSign(y)); /* truncate everything */
+			return 0;
+		}
         exptoadd = -nf;
         nf = 0;
     }
+
     /* ix: x->fraq[ix] contains round position */
     ix = nf/(int)BASE_FIG;
-    if(((U_LONG)ix)>=y->Prec) return 0; /* Unable to round */
+    if(((U_LONG)ix)>=y->Prec) return 0;  /* rounding position too right(small). */
     ioffset = nf - ix*((int)BASE_FIG);
 
     v = y->frac[ix];
+
     /* drop digits after pointed digit */
     n = BASE_FIG - ioffset - 1;
     for(shifter=1,i=0;i<n;++i) shifter *= 10;