diff --git a/yasnippet-tests.el b/yasnippet-tests.el
index 582619e..2d92765 100644
--- a/yasnippet-tests.el
+++ b/yasnippet-tests.el
@@ -121,7 +121,8 @@ This lets `yas--maybe-expand-from-keymap-filter' work as expected."
         (funcall fn)
       (cl-loop for var in vars
                for saved in saved-values
-               do (set var saved)))))
+               do (unless (eq (symbol-value var) saved) ;Beware read-only vars!
+                    (set var saved))))))
 
 (defun yas-call-with-snippet-dirs (dirs fn)
   (let* ((default-directory (make-temp-file "yasnippet-fixture" t))
@@ -1229,11 +1230,11 @@ hello ${1:$(when (stringp yas-text) (funcall func yas-text))} foo${1:$$(concat \
   (let ((saved-sym (make-symbol "yas--buffer-list")))
     `(let ((,saved-sym (symbol-function 'buffer-list)))
        (cl-letf (((symbol-function 'buffer-list)
-                  (lambda ()
+                  (lambda (&rest args)
                     (cl-remove-if (lambda (buf)
                                     (with-current-buffer buf
                                       (eq major-mode 'lisp-interaction-mode)))
-                                  (funcall ,saved-sym)))))
+                                  (apply ,saved-sym args)))))
          ,@body))))
 
 
@@ -1386,19 +1387,14 @@ hello ${1:$(when (stringp yas-text) (funcall func yas-text))} foo${1:$$(concat \
                           yet-another-c-mode
                           and-also-this-one
                           and-that-one
-                          ;; prog-mode doesn't exist in emacs 23.4
-                          ,@(if (fboundp 'prog-mode)
-                                '(prog-mode))
-                          ;; lisp-data-mode doesn't exist in emacs 27.1
-                          ,@(if (fboundp 'lisp-data-mode)
+                          prog-mode
+                          ,@(if (fboundp 'lisp-data-mode) ;Emacs≥28
                                 '(lisp-data-mode))
                           emacs-lisp-mode
-                          lisp-interaction-mode
-                          ;; `lisp-data-mode' doesn't exist prior to Emacs 28.
-                          ,@(and (fboundp 'lisp-data-mode) '(lisp-data-mode))))
+                          lisp-interaction-mode))
               (observed (yas--modes-to-activate)))
          (should (equal major-mode (car observed)))
-         (should (equal (sort expected #'string<) (sort observed #'string<))))))))
+         (should-not (cl-set-exclusive-or expected observed)))))))
 
 (ert-deftest extra-modes-parenthood ()
   "Test activation of parents of `yas--extra-modes'."
@@ -1415,27 +1411,21 @@ hello ${1:$(when (stringp yas-text) (funcall func yas-text))} foo${1:$$(concat \
        (yas-activate-extra-mode 'and-that-one)
        (let* ((expected-first `(and-that-one
                                 yet-another-c-mode
-                                c-mode
-                                ,major-mode))
+                                c-mode))
               (expected-rest `(cc-mode
-                               ;; prog-mode doesn't exist in emacs 23.4
-                               ,@(if (fboundp 'prog-mode)
-                                     '(prog-mode))
-                               ;; lisp-data-mode doesn't exist in emacs 27.1
-                               ,@(if (fboundp 'lisp-data-mode)
+                               prog-mode
+                               ,@(if (fboundp 'lisp-data-mode) ;Emacs≥28
                                      '(lisp-data-mode))
                                emacs-lisp-mode
                                and-also-this-one
-                               lisp-interaction-mode
-                               ;; `lisp-data-mode' doesn't exist prior to
-                               ;; Emacs 28.
-                               ,@(and (fboundp 'lisp-data-mode)
-                                      '(lisp-data-mode))))
-              (observed (yas--modes-to-activate)))
-         (should (equal expected-first
-                        (cl-subseq observed 0 (length expected-first))))
-         (should (equal (sort expected-rest #'string<)
-                        (sort (cl-subseq observed (length expected-first)) #'string<))))))))
+                               lisp-interaction-mode))
+              (observed (remq 'fundamental-mode (yas--modes-to-activate))))
+         (should-not (cl-set-exclusive-or
+                      expected-first
+                      (cl-subseq observed 0 (length expected-first))))
+         (should-not (cl-set-exclusive-or
+                      expected-rest
+                      (cl-subseq observed (length expected-first)))))))))
 
 (defalias 'yas--phony-c-mode #'c-mode)
 
diff --git a/yasnippet.el b/yasnippet.el
index 0641d0d..980a585 100644
--- a/yasnippet.el
+++ b/yasnippet.el
@@ -828,10 +828,12 @@ which decides on the snippet to expand.")
                                       (mapcar #'yas--all-parents
                                               (gethash parent yas--parents))))
                                    ap)))
-                     (yas--merge-ordered-lists
-                      (cons (if (eq (car ap) 'fundamental-mode) ap
-                              (append ap '(fundamental-mode)))
-                            extras)))
+                     (cl-assert (eq mode (car ap)))
+                     (cons mode
+                           (yas--merge-ordered-lists
+                            (cons (if (eq mode 'fundamental-mode) ()
+                                    (append (cdr ap) '(fundamental-mode)))
+                                  extras))))
                  (cons mode
                        (yas--merge-ordered-lists
                         (mapcar #'yas--all-parents
@@ -851,15 +853,15 @@ which decides on the snippet to expand.")
   "Compute list of mode symbols that are active for `yas-expand' and friends."
   (let* ((modes
           (delete-dups
-           (remq nil `(,(or mode major-mode)
+           (remq nil `(,@(unless mode yas--extra-modes)
+                       ,(or mode major-mode)
                        ;; FIXME: Alternative major modes should use
                        ;; `derived-mode-add-parents', but until that
                        ;; becomes common, use `major-mode-remap-alist'
                        ;; as a crutch to supplement the mode hierarchy.
                        ,(and (boundp 'major-mode-remap-alist)
                              (car (rassq (or mode major-mode)
-                                         major-mode-remap-alist)))
-                       ,@(unless mode (reverse yas--extra-modes)))))))
+                                         major-mode-remap-alist))))))))
     (yas--merge-ordered-lists
      (mapcar #'yas--all-parents modes))))
 
@@ -1281,7 +1283,7 @@ Return TEMPLATE."
       (cl-assert menu-keymap)
       (yas--delete-from-keymap menu-keymap (yas--template-uuid template))
 
-      ;; Add necessary subgroups as necessary.
+      ;; Add subgroups as necessary.
       ;;
       (dolist (subgroup group)
         (let ((subgroup-keymap (lookup-key menu-keymap (vector (make-symbol subgroup)))))
@@ -1491,7 +1493,7 @@ Also tries to work around Emacs Bug#30931."
   (yas--safely-call-fun (apply-partially #'eval form)))
 
 (defun yas--read-lisp (string &optional nil-on-error)
-  "Read STRING as a elisp expression and return it.
+  "Read STRING as an Elisp expression and return it.
 
 In case STRING in an invalid expression and NIL-ON-ERROR is nil,
 return an expression that when evaluated will issue an error."