diff --git a/asdf.asd b/asdf.asd
index e36a34e9293edad17bc1cee717b66a725d1bf3ad..3fba33a41e8f4c1b2fad09ee8ec9e6393d991750 100644
--- a/asdf.asd
+++ b/asdf.asd
@@ -15,7 +15,7 @@
   :licence "MIT"
   :description "Another System Definition Facility"
   :long-description "ASDF builds Common Lisp software organized into defined systems."
-  :version "2.26.98" ;; to be automatically updated by bin/bump-revision
+  :version "2.26.99" ;; to be automatically updated by bin/bump-revision
   :depends-on ()
   :components ((:module "build" :components ((:file "asdf"))))
   :in-order-to (#+asdf2.27 (compile-op (monolithic-load-concatenated-source-op generate-asdf))))
diff --git a/header.lisp b/header.lisp
index f1bccd1597c32314bdd04310c65d7f21a62343b9..b878ff31581f30df60ff6461fc456e508401bfa9 100644
--- a/header.lisp
+++ b/header.lisp
@@ -1,5 +1,5 @@
 ;; -*- mode: Common-Lisp; Base: 10 ; Syntax: ANSI-Common-Lisp ; coding: utf-8 -*-
-;;; This is ASDF 2.26.98: Another System Definition Facility.
+;;; This is ASDF 2.26.99: Another System Definition Facility.
 ;;;
 ;;; Feedback, bug reports, and patches are all welcome:
 ;;; please mail to <asdf-devel@common-lisp.net>.
diff --git a/package.lisp b/package.lisp
index 43bbea2a3a66a2c1a0674e945d8927fb8e43ae39..37535648834249bf0be68221f776b27d5144ac76 100644
--- a/package.lisp
+++ b/package.lisp
@@ -299,16 +299,16 @@ or when loading the package is optional."
       (setf *package-fishiness* nil)))
   (defun record-fishy (info)
     (push info *package-fishiness*))
-  (macrolet ((when-fishy (&body body)
-               `(when *all-package-fishiness* ,@body))
-             (fishy (&rest info)
-               `(when-fishy (record-fishy (list ,@info)))))
-    (defun ensure-package (name &key
-                                  nicknames documentation use
-                                  shadow shadowing-import-from
-                                  import-from export intern
-                                  recycle mix reexport
-                                  unintern)
+  (defun ensure-package (name &key
+                                nicknames documentation use
+                                shadow shadowing-import-from
+                                import-from export intern
+                                recycle mix reexport
+                                unintern)
+    (macrolet ((when-fishy (&body body)
+                 `(when *all-package-fishiness* ,@body))
+               (fishy (&rest info)
+                 `(when-fishy (record-fishy (list ,@info)))))
       (let* ((name (string name))
              (nicknames (mapcar #'string nicknames))
              (names (cons name nicknames))
@@ -579,15 +579,18 @@ or when loading the package is optional."
      (apply 'ensure-package ',(parse-define-package-form package clauses))))
 
 
-;;; Final tricks to keep various implementations happier
+;;;; Final tricks to keep various implementations happy.
 (eval-when (:load-toplevel :compile-toplevel :execute)
   #+allegro
   (setf excl::*autoload-package-name-alist*
         (remove "asdf" excl::*autoload-package-name-alist*
                 :test 'equalp :key 'car)) ; We need that BEFORE any mention of package ASDF.
-  (unless (member :asdf2.27 *features*)
-    #+(or clisp xcl)
-    (progn
-      (when (find-package :asdf)
-        (delete-package* :asdf t))
-      (make-package :asdf :use ()))))
+  #+(or clisp xcl)
+  (unless (let ((vs (find-symbol* 'version-satisfies :asdf nil))
+                (av (find-symbol* 'asdf-version :asdf nil)))
+            (and vs av (funcall vs (funcall av) "2.26.59")))
+    (when (find-package :asdf)
+      (delete-package* :asdf t))
+    (make-package :asdf :use ())))
+
+
diff --git a/pathname.lisp b/pathname.lisp
index 9b062848f33aa84746b7e179740adcfc2b45e6de..962e298777f357fe39dad87b3ee4c38bae1ee638 100644
--- a/pathname.lisp
+++ b/pathname.lisp
@@ -271,7 +271,7 @@ actually-existing directory."
                   :defaults defaults))
 
 (defmacro with-pathname-defaults ((&optional defaults) &body body)
-  `(let ((*default-pathname-defaults* ,(or defaults (nil-pathname)))) ,@body))
+  `(let ((*default-pathname-defaults* ,(or defaults '(nil-pathname)))) ,@body))
 
 (defun* truename* (p)
   ;; avoids both logical-pathname merging and physical resolution issues
diff --git a/test/run-tests.sh b/test/run-tests.sh
index 1bf21f0397c5649a6ed4ec125f86e701450d1bac..57c41ce3235fb46c3245af177d10a61b2e0887a8 100755
--- a/test/run-tests.sh
+++ b/test/run-tests.sh
@@ -211,20 +211,34 @@ upgrade_tags () {
     if [ -n "$TEST_ASDF_TAGS" ] ; then
         echo $TEST_ASDF_TAGS ; return
     fi
+    # REQUIRE is a magic tag meaning whatever your implementation provides
     # 1.37 is the last release by Daniel Barlow
     # 1.97 is the last release before Gary King takes over
     # 1.369 is the last release by Gary King
     # 2.000 to 2.019 and 2.20 to 2.27 and beyond are Faré's "stable" releases
-    echo 1.37 1.97 1.369
+    # 2.26.61 is the last single-package ASDF.
+    echo REQUIRE 1.37 1.97 1.369 2.26.61
     git tag -l '2.0??'
     git tag -l '2.??'
 }
+upgrade_methods () {
+    if [ -n "$TEST_ASDF_METHODS" ] ; then
+        echo $TEST_ASDF_METHODS ; return
+    fi
+    cat <<EOF
+'load-asdf-lisp'load-asdf-system
+'load-asdf-lisp'compile-load-asdf
+'load-asdf-lisp'load-asdf-fasl
+()'load-asdf-fasl
+EOF
+}
 extract_tagged_asdf () {
     ver=$1
+    if [ REQUIRE = "$ver" ] ; then return 0 ; fi
     file=build/asdf-${tag}.lisp ;
     if [ ! -f $file ] ; then
         case $ver in
-            1.*|2.0*|2.2[0-6])
+            1.*|2.0*|2.2[0-6]|2.26.61)
                 git show ${tag}:asdf.lisp > $file ;;
             *)
                 echo "Don't know how to extract asdf.lisp for version $tag"
@@ -243,7 +257,7 @@ valid_upgrade_test_p () {
             # my old ubuntu clisp 2.44.1 is wired in with an antique ASDF 1 from CLC that can't be downgraded.
             # 2.00[0-7] use UID, which fails on that CLISP and was removed afterwards.
             # Note that for the longest time, CLISP has included 2.011 in its distribution.
-            : ;; 
+            : ;;
         cmucl:1.*|cmucl:2.00*|cmucl:2.01[0-4]:*)
             : Skip, CMUCL has problems before 2.014.7 due to source-registry upgrade ;;
         ecl*:1.*|ecl*:2.0[01]*|ecl*:2.20:*)
@@ -256,16 +270,17 @@ valid_upgrade_test_p () {
         *) return 0 ;;
    esac
    return 1
-}    
+}
 run_upgrade_tests () {
     su=test/script-support.lisp
-    lv="$command $eval (load\"$su\") $eval" ;
     for tag in `upgrade_tags` ; do
-        for x in load-asdf-system load-asdf-lisp compile-load-asdf load-asdf-fasl just-load-asdf-fasl ; do
-            if valid_upgrade_test_p $lisp $tag $x ; then
-                echo "Testing upgrade from ASDF ${tag} using method $x" ;
-                $lv "(asdf-test::test-upgrade 'asdf-test::$x \"$tag\")" ||
-                { echo "upgrade FAILED for $lisp from $tag using method $x" ; exit 1 ;}
+        for method in `upgrade_methods` ; do
+            if valid_upgrade_test_p $lisp $tag $method ; then
+                echo "Testing ASDF upgrade from ${tag} using method $method"
+                extract_tagged_asdf $tag
+                $command $eval \
+                "'(#.(load\"$su\")#.(in-package :asdf-test)#.(test-upgrade $method \"$tag\"))" ||
+                { echo "upgrade FAILED for $lisp from $tag using method $method" ; exit 1 ;}
     fi ; done ; done 2>&1 | tee build/results/${lisp}-upgrade.text
 }
 run_tests () {
diff --git a/test/script-support.lisp b/test/script-support.lisp
index 51ea0765e8aa42dd02d9916ce7c065d60575658f..e3f9c9606177fba4c09f54e34cea0ba099cb672c 100644
--- a/test/script-support.lisp
+++ b/test/script-support.lisp
@@ -345,13 +345,20 @@ is bound, write a message and exit on an error.  If
     (register-directory *test-directory*)
     (acall :oos (asym :load-op) x :verbose verbose)))
 
-(defun test-upgrade (method tag) ;; called by run-test
+(defun test-upgrade (old-method new-method tag) ;; called by run-test
   (with-test ()
-    (unless (eq method 'just-load-asdf-fasl)
-      (format t "Loading old asdf ~A~%" tag)
-      (load-asdf-lisp tag))
-    (format t "Loading new asdf with method ~A~%" method)
-    (funcall method)
+    (when old-method
+      (cond
+        ((equal tag "REQUIRE")
+         (format t "Requiring some previous asdf ~A~%" tag)
+         (ignore-errors (funcall 'require "asdf"))
+         (unless (member "ASDF" *modules* :test 'equal)
+           (leave-test "Your Lisp implementation does not provide ASDF. Skipping test.~%" 0)))
+        (t
+         (format t "Loading old asdf ~A via ~A~%" tag old-method)
+         (funcall old-method tag))))
+    (format t "Now loading new asdf via method ~A~%" new-method)
+    (funcall new-method)
     (format t "Testing it~%")
     (register-directory *test-directory*)
     (load-test-system :test-module-depend)
diff --git a/upgrade.lisp b/upgrade.lisp
index be262b5c1e1a5bab6a1b39b1322c7e378442ddc8..e8f6088cd0fe6a469d9e9d7153a1cb92f514707b 100644
--- a/upgrade.lisp
+++ b/upgrade.lisp
@@ -35,7 +35,7 @@
          ;; "2.345.6" would be a development version in the official upstream
          ;; "2.345.0.7" would be your seventh local modification of official release 2.345
          ;; "2.345.6.7" would be your seventh local modification of development version 2.345.6
-         (asdf-version "2.26.98")
+         (asdf-version "2.26.99")
          (existing-asdf (find-class (find-symbol* :component :asdf nil) nil))
          (existing-version *asdf-version*)
          (already-there (equal asdf-version existing-version)))
diff --git a/utility.lisp b/utility.lisp
index c0512481b28dbb151b0ea34e508b698b369c112c..3e1cc79fd635613d9ecd37c23c75a47ec20a3970 100644
--- a/utility.lisp
+++ b/utility.lisp
@@ -34,7 +34,7 @@
   (defun undefine-function (function-spec)
     (cond
       ((symbolp function-spec)
-       #+clisp
+       #+(and clisp (or))
        (let ((f (and (fboundp function-spec) (fdefinition function-spec))))
          (when (typep f 'clos:standard-generic-function)
            (loop :for m :in (clos:generic-function-methods f)
@@ -51,7 +51,12 @@
     ((defdef (def* def)
        `(defmacro ,def* (name formals &rest rest)
           `(progn
-             #-clisp ;; clisp is unhappy about fmakunbound.
+             ;; undefining the previous function is the portable way
+             ;; of overriding any incompatible previous gf, but somehow
+             ;; this causes CLISP to fail to see COMPONENT-NAME methods after ugprade
+             ;; so instead, for CLISP we delete-package* in package.lisp
+             ;; any time the API changes.
+             #-clisp
              (undefine-function ',name)
              #-gcl ; gcl 2.7.0 notinline functions lose secondary return values :-(
              ,@(when (and #+ecl (symbolp name)) ; fails for setf functions on ecl
diff --git a/version.lisp-expr b/version.lisp-expr
index 11a7c42870dcf3c6d06eea1bab705556bf5d9d99..ed17e9f99b40a5ca45c76698100819130c63032c 100644
--- a/version.lisp-expr
+++ b/version.lisp-expr
@@ -1 +1 @@
-"2.26.98"
+"2.26.99"