diff --git a/src/pcl/defcombin.lisp b/src/pcl/defcombin.lisp
index f1dd88141..cad4e426d 100644
--- a/src/pcl/defcombin.lisp
+++ b/src/pcl/defcombin.lisp
@@ -102,9 +102,9 @@
                               (short-combine-methods type-name options operator ioa source-location doc))))
         (old-info (gethash type-name **method-combinations**)))
     (flet ((frobber (mc)
-             ;; KLUDGE: assume the MC is already a short-form MC
-             (reinitialize-instance mc :operator operator :identity-with-one-argument ioa
-                                    'source source-location :documentation doc)))
+             (change-class mc 'short-method-combination
+                           :operator operator :identity-with-one-argument ioa
+                           'source source-location :documentation doc)))
       (update-mcs type-name info old-info #'frobber)))
   (setf (random-documentation type-name 'method-combination) doc)
   type-name)
@@ -185,9 +185,9 @@
                :source-location source-location))
         (old-info (gethash type-name **method-combinations**)))
     (flet ((frobber (mc)
-             (reinitialize-instance mc :type-name type-name
-                                    :args-lambda-list args-lambda-list
-                                    'source source-location :documentation doc)))
+             (change-class mc 'long-method-combination
+                           :type-name type-name :args-lambda-list args-lambda-list
+                           'source source-location :documentation doc)))
       (update-mcs type-name info old-info #'frobber)))
   (setf (gethash type-name *long-method-combination-functions*) function)
   (setf (random-documentation type-name 'method-combination) doc)
diff --git a/tests/clos-method-combination-redefinition.impure.lisp b/tests/clos-method-combination-redefinition.impure.lisp
index 1b8013ded..a4526e4ad 100644
--- a/tests/clos-method-combination-redefinition.impure.lisp
+++ b/tests/clos-method-combination-redefinition.impure.lisp
@@ -168,13 +168,32 @@
   (assert (not (even-as (make-instance 'parse-state :string "abcbabab"))))
   (assert (even-as (make-instance 'parse-state :string "abcbabab") :start 'no)))
 
-;;; TODO
-;;;
-;;; 4. (possibly) move long-method-combination-function into method
-;;;    combination objects, in which case need to check that existing
-;;;    method combination objects are updated (currently the method
-;;;    combination function lives in a global hash table and that is
-;;;    updated at redefinition time).
-;;;
-;;; 5. redefinition between short- and long-form method combinations
+;;;; changing between short- and long-form method combination
+(define-method-combination maximum :operator max)
 
+(defgeneric maxx (x)
+  (:method-combination maximum)
+  (:method maximum ((x symbol)) 3)
+  (:method maximum ((x list)) 4)
+  (:method maximum ((x null)) 5))
+
+(with-test (:name (:method-combination :maximum))
+  (assert (= (maxx nil) 5))
+  (assert (= (maxx '(3 4)) 4))
+  (assert (= (maxx t) 3)))
+
+(define-method-combination maximum ()
+  ((maximum (maximum)))
+  `(min ,@(mapcar (lambda (m) `(call-method ,m)) maximum)))
+
+(with-test (:name (:method-combination :maximum :redefined-long))
+  (assert (= (maxx nil) 3))
+  (assert (= (maxx '(3 4)) 4))
+  (assert (= (maxx t) 3)))
+
+(define-method-combination maximum :operator -)
+
+(with-test (:name (:method-combination :maximum :redefined-short))
+  (assert (= (maxx nil) -2))
+  (assert (= (maxx '(3 4)) -4))
+  (assert (= (maxx t) -3)))