diff --git a/ChangeLog b/ChangeLog
index f60fc4b6aa..717221dc4f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jul 10 22:44:19 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c: Add a static assertion for RBIGNUM_EMBED_LEN_MAX.
+
 Wed Jul 10 22:31:25 2013  Masaki Matsushita  <glass.saga@gmail.com>
 
 	* string.c (rb_str_index): cache single byte flag and some
diff --git a/bignum.c b/bignum.c
index 3f5ea1745f..c37bf92c6d 100644
--- a/bignum.c
+++ b/bignum.c
@@ -45,6 +45,7 @@ static VALUE big_three = Qnil;
 #endif
 
 STATIC_ASSERT(sizeof_bdigit_dbl, sizeof(BDIGIT_DBL) == SIZEOF_BDIGIT_DBL);
+STATIC_ASSERT(rbignum_embed_len_max, RBIGNUM_EMBED_LEN_MAX <= (RBIGNUM_EMBED_LEN_MASK >> RBIGNUM_EMBED_LEN_SHIFT));
 
 #ifdef WORDS_BIGENDIAN
 #   define HOST_BIGENDIAN_P 1