diff --git a/ChangeLog b/ChangeLog
index 218733799d..4fd2c21ae7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Fri Jun 21 18:56:58 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (bigsub_int): Use bdigit_roomof.
+	  (bigadd_int): Ditto.
+	  (bigand_int): Ditto.
+	  (bigor_int): Ditto.
+	  (bigxor_int): Ditto.
+
 Fri Jun 21 17:56:25 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* benchmark/gc/gcbench.rb: fix summary of benchmark result notaton.
diff --git a/bignum.c b/bignum.c
index 1c2b8dc999..730eb6a6af 100644
--- a/bignum.c
+++ b/bignum.c
@@ -2975,7 +2975,7 @@ bigsub_int(VALUE x, long y0)
     i = 1;
 #else
     num = 0;
-    for (i=0; i<(int)(sizeof(y)/SIZEOF_BDIGITS); i++) {
+    for (i=0; i<bdigit_roomof(SIZEOF_LONG); i++) {
 	num += (BDIGIT_DBL_SIGNED)xds[i] - BIGLO(y);
 	zds[i] = BIGLO(num);
 	num = BIGDN(num);
@@ -3026,7 +3026,7 @@ bigadd_int(VALUE x, long y)
     i = 1;
 #else
     num = 0;
-    for (i=0; i<(int)(sizeof(y)/SIZEOF_BDIGITS); i++) {
+    for (i=0; i<bdigit_roomof(SIZEOF_LONG); i++) {
 	num += (BDIGIT_DBL)xds[i] + BIGLO(y);
 	zds[i] = BIGLO(num);
 	num = BIGDN(num);
@@ -4439,7 +4439,7 @@ bigand_int(VALUE x, long y)
     {
 	BDIGIT_DBL num = y;
 
-	for (i=0; i<(int)(sizeof(y)/SIZEOF_BDIGITS); i++) {
+	for (i=0; i<bdigit_roomof(SIZEOF_LONG); i++) {
 	    zds[i] = xds[i] & BIGLO(num);
 	    num = BIGDN(num);
 	}
@@ -4535,7 +4535,7 @@ bigor_int(VALUE x, long y)
     {
 	BDIGIT_DBL num = y;
 
-	for (i=0; i<(int)(sizeof(y)/SIZEOF_BDIGITS); i++) {
+	for (i=0; i<bdigit_roomof(SIZEOF_LONG); i++) {
 	    zds[i] = xds[i] | BIGLO(num);
 	    num = BIGDN(num);
 	}
@@ -4631,7 +4631,7 @@ bigxor_int(VALUE x, long y)
     {
 	BDIGIT_DBL num = y;
 
-	for (i=0; i<(int)(sizeof(y)/SIZEOF_BDIGITS); i++) {
+	for (i=0; i<bdigit_roomof(SIZEOF_LONG); i++) {
 	    zds[i] = xds[i] ^ BIGLO(num);
 	    num = BIGDN(num);
 	}