diff --git a/lisp/gnus/ChangeLog b/lisp/gnus/ChangeLog
index 14734e3e40d..591c6446ec0 100644
--- a/lisp/gnus/ChangeLog
+++ b/lisp/gnus/ChangeLog
@@ -1,3 +1,9 @@
+2015-04-06  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Use American spelling for 'normalize'
+	* rtree.el (rtree-normalize-range): Rename from rtree-normalise-range.
+	All uses changed.  Add an alias for obsolete usages.
+
 2015-04-03  Katsumi Yamaoka  <yamaoka@jpl.org>
 
 	* gnus-art.el (gnus-article-browse-html-save-cid-content):
diff --git a/lisp/gnus/rtree.el b/lisp/gnus/rtree.el
index 59c17ae50b6..001c6ed1de2 100644
--- a/lisp/gnus/rtree.el
+++ b/lisp/gnus/rtree.el
@@ -79,11 +79,14 @@
 (defmacro rtree-range (node)
   `(car ,node))
 
-(defsubst rtree-normalise-range (range)
+(defsubst rtree-normalize-range (range)
   (when (numberp range)
     (setq range (cons range range)))
   range)
 
+(define-obsolete-function-alias rtree-normalise-range
+  rtree-normalize-range "25.1")
+
 (defun rtree-make (range)
   "Make an rtree from RANGE."
   ;; Normalize the range.
@@ -96,7 +99,7 @@
 	(node (rtree-make-node)))
     (when (> mid 0)
       (rtree-set-left node (rtree-make-1 range mid)))
-    (rtree-set-range node (rtree-normalise-range (cadr range)))
+    (rtree-set-range node (rtree-normalize-range (cadr range)))
     (setcdr range (cddr range))
     (when (> (- length mid 1) 0)
       (rtree-set-right node (rtree-make-1 range (- length mid 1))))