diff --git a/ChangeLog b/ChangeLog
index 535f747d00..7b60407795 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sat Feb 27 15:54:55 2010  Tanaka Akira  <akr@fsij.org>
+
+	* pack.c: check assuption on QUAD_SIZE and SIZEOF_LONG.
+
+	* bignum.c: check assuption on SIZEOF_LONG and SIZEOF_BDIGITS.
+
 Sat Feb 27 03:48:18 2010  Tanaka Akira  <akr@fsij.org>
 
 	* pack.c: fix q and Q for big endian environments which have no
diff --git a/bignum.c b/bignum.c
index 451ed5a8e0..d316a60d82 100644
--- a/bignum.c
+++ b/bignum.c
@@ -304,6 +304,10 @@ rb_int2inum(SIGNED_VALUE n)
     return rb_int2big(n);
 }
 
+#if SIZEOF_LONG % SIZEOF_BDIGITS != 0
+# error unexpected SIZEOF_LONG : SIZEOF_BDIGITS ratio
+#endif
+
 void
 rb_big_pack(VALUE val, unsigned long *buf, long num_longs)
 {
diff --git a/pack.c b/pack.c
index 552350c864..734dc96660 100644
--- a/pack.c
+++ b/pack.c
@@ -740,6 +740,9 @@ pack_pack(VALUE ary, VALUE fmt)
 #endif
 
 #if SIZEOF_LONG != QUAD_SIZE || defined(FORCE_BIG_PACK)
+#if QUAD_SIZE % SIZEOF_LONG != 0
+# error unexpected QUAD_SIZE : SIZEOF_LONG ratio
+#endif
               case QUAD_SIZE:
                 while (len-- > 0) {
                     unsigned long tmp[QUAD_SIZE/SIZEOF_LONG];
@@ -1662,6 +1665,9 @@ pack_unpack(VALUE str, VALUE fmt)
 #endif
 
 #if (SIZEOF_LONG != QUAD_SIZE && (!defined(HAVE_LONG_LONG) || SIZEOF_LONG_LONG != QUAD_SIZE)) || defined(FORCE_BIG_PACK)
+#if QUAD_SIZE % SIZEOF_LONG != 0
+# error unexpected QUAD_SIZE : SIZEOF_LONG ratio
+#endif
 	      case QUAD_SIZE:
 		if (bigendian_p != BIGENDIAN_P())
 		    rb_bug("unexpected endian for unpack");