diff --git a/ChangeLog b/ChangeLog
index a08a2a4745..53fc83d40b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Nov 21 21:40:00 2013  Kenta Murata  <mrkn@mrkn.jp>
+
+	* ext/bigdecimal/bigdecimal.c (VpAlloc): Fix the expr to adjust the size
+	  of the digit array.
+
 Thu Nov 21 21:36:00 2013  Kenta Murata  <mrkn@mrkn.jp>
 
 	* ext/bigdecimal/bigdecimal.c (BigDecimal_sqrt): Fix the precision of
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 53efafd24b..533333228a 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -3816,7 +3816,9 @@ VpAlloc(size_t mx, const char *szVal)
     size_t mf = VpGetPrecLimit();
     VALUE buf;
 
-    mx = (mx + BASE_FIG - 1) / BASE_FIG + 1;    /* Determine allocation unit. */
+    mx = (mx + BASE_FIG - 1) / BASE_FIG;    /* Determine allocation unit. */
+    if (mx == 0) ++mx;
+
     if (szVal) {
 	while (ISSPACE(*szVal)) szVal++;
 	if (*szVal != '#') {