diff --git a/ChangeLog b/ChangeLog
index 7faa4e2297..720bbcd102 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Jun 21 21:20:31 2006  Tadayoshi Funaba  <tadf@dotrb.org>
+
+	* lib/date.rb (jd_to_commercial): now works fine even if in
+	  mathn-ized context.
+
 Wed Jun 21 17:29:57 2006  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* ext/socket/getaddrinfo.c (freeaddrinfo, get_name): fixed typo.
diff --git a/lib/date.rb b/lib/date.rb
index 93419091ae..722ecd154e 100644
--- a/lib/date.rb
+++ b/lib/date.rb
@@ -1,7 +1,7 @@
 #
 # date.rb - date and time library
 #
-# Author: Tadayoshi Funaba 1998-2005
+# Author: Tadayoshi Funaba 1998-2006
 #
 # Documentation: William Webber <william@williamwebber.com>
 #
@@ -370,7 +370,7 @@ class Date
     ns = ns?(jd, sg)
     a = jd_to_civil(jd - 3, ns)[0]
     y = if jd >= commercial_to_jd(a + 1, 1, 1, ns) then a + 1 else a end
-    w = 1 + (jd - commercial_to_jd(y, 1, 1, ns)) / 7
+    w = 1 + ((jd - commercial_to_jd(y, 1, 1, ns)) / 7).floor
     d = (jd + 1) % 7
     if d.zero? then d = 7 end
     return y, w, d