diff --git a/lisp/gnus/ChangeLog b/lisp/gnus/ChangeLog
index baabe5f65b9..f40f65063a2 100644
--- a/lisp/gnus/ChangeLog
+++ b/lisp/gnus/ChangeLog
@@ -1,3 +1,8 @@
+2011-04-11  Katsumi Yamaoka  <yamaoka@jpl.org>
+
+	* gnus-art.el (article-treat-date): Assume that
+	gnus-article-date-headers may be a group parameter.
+
 2011-04-07  Teodor Zlatanov  <tzz@lifelogs.com>
 
 	* gnus-registry.el (gnus-registry-handle-action): More debugging.
diff --git a/lisp/gnus/gnus-art.el b/lisp/gnus/gnus-art.el
index 97677988f0a..e03c787d995 100644
--- a/lisp/gnus/gnus-art.el
+++ b/lisp/gnus/gnus-art.el
@@ -3407,7 +3407,11 @@ lines forward."
 	(setq ended t)))))
 
 (defun article-treat-date ()
-  (article-date-ut gnus-article-date-headers t))
+  (article-date-ut (if (gnus-buffer-live-p gnus-summary-buffer)
+		       (with-current-buffer gnus-summary-buffer
+			 gnus-article-date-headers)
+		     gnus-article-date-headers)
+		   t))
 
 (defun article-date-ut (&optional type highlight date-position)
   "Convert DATE date to TYPE in the current article.