diff --git a/etc/NEWS b/etc/NEWS
index c0e404f8106..0e2a6849ca6 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -4011,11 +4011,11 @@ that will provide an Xref backend when used.
 
 +++
 ** The API to manipulate error descriptors has been improved.
-there are new functions: 'error-type-p', 'error-type',
+There are new functions: 'error-type-p', 'error-type',
 'error-has-type-p', and 'error-slot-value'.
-And you can now do (signal err) instead (signal (car err) (cdr err)), which
-is not just more concise but also preserves the 'eq'uality of the
-error descriptor.
+And you can now do '(signal err)' instead of
+'(signal (car err) (cdr err))', which is not only more concise
+but also preserves the 'eq'uality of the error descriptor.
 
 +++
 ** 'secure-hash' now supports generating SHA-3 message digests.
diff --git a/lisp/emacs-lisp/ert.el b/lisp/emacs-lisp/ert.el
index 6dacd568c7a..1c2df07f137 100644
--- a/lisp/emacs-lisp/ert.el
+++ b/lisp/emacs-lisp/ert.el
@@ -399,8 +399,8 @@ and aborts the current test as failed if it doesn't."
   (let ((handled-conditions (pcase-exhaustive type
                               ((pred listp) type)
                               ((pred symbolp) (list type)))))
-    (unless (cl-some (lambda (hc) (error-has-type-p condition hc))
-                     handled-conditions)
+    (unless (any (lambda (hc) (error-has-type-p condition hc))
+                 handled-conditions)
       (ert-fail (append
                  (funcall form-description-fn)
                  (list
diff --git a/lisp/epa-file.el b/lisp/epa-file.el
index e45dbd1754e..b2a89907867 100644
--- a/lisp/epa-file.el
+++ b/lisp/epa-file.el
@@ -116,7 +116,7 @@ encryption is used."
 (defun epa-file--find-file-not-found-function ()
   (let ((error epa-file-error))
     (save-window-excursion
-     (kill-buffer))
+      (kill-buffer))
     ;; FIXME: How do we know that slot 3 can hold only a message related
     ;; to a wrong passphrase?
     (if (error-slot-value error 3)
@@ -140,8 +140,9 @@ encryption is used."
           error-string)
          (match-string 1 error-string))))
 
-(defun epa-file--error-add-context (err ctxt)
-  (setf (cdr error) (append (cdr error) (list ctx))))
+(defun epa-file--error-add-context (error context)
+  "Append CONTEXT to ERROR data by side effect."
+  (setf (cdr error) (append (cdr error) (list context))))
 
 (defvar last-coding-system-used)
 (defun epa-file-insert-file-contents (file &optional visit beg end replace)
diff --git a/lisp/ffap.el b/lisp/ffap.el
index aa8dffc9dcd..800437d69c9 100644
--- a/lisp/ffap.el
+++ b/lisp/ffap.el
@@ -474,8 +474,8 @@ Returned values:
               ;; (file-error "Connection failed" "address already in use"
 	      ;;	     "ftp.uu.net" "ffap-machine-p")
 	      ((equal mesg "connection failed")
-	       (if (string= (downcase (error-slot-value error 2))
-		            "permission denied")
+               (if (string-equal-ignore-case (error-slot-value error 2)
+                                             "permission denied")
 		   nil			; host does not exist
 		 ;; Other errors mean the host exists:
 		 (error-slot-value error 2)))
diff --git a/lisp/gnus/gnus-search.el b/lisp/gnus/gnus-search.el
index 76626541bf2..2e9adeec23d 100644
--- a/lisp/gnus/gnus-search.el
+++ b/lisp/gnus/gnus-search.el
@@ -2087,7 +2087,7 @@ Assume \"size\" key is equal to \"larger\"."
 	      (apply #'nnheader-message 4
 		     "Search engine for %s improperly configured: %s"
 		     server (error-slot-value err 1))
-	    (signal err err)))))
+            (signal err)))))
      (alist-get 'search-group-spec specs))
     ;; Some search engines do their own limiting, but some don't, so
     ;; do it again here.  This is bad because, if the user is
diff --git a/lisp/gnus/nnmaildir.el b/lisp/gnus/nnmaildir.el
index bb80c2551ae..750ebc413b6 100644
--- a/lisp/gnus/nnmaildir.el
+++ b/lisp/gnus/nnmaildir.el
@@ -364,7 +364,7 @@ This variable is set by `nnmaildir-request-article'.")
 
 (defun nnmaildir--emlink-p (err)
   (and (error-has-type-p err 'file-error)
-       (string= (downcase (error-slot-value err 2)) "too many links")))
+       (string-equal-ignore-case (error-slot-value err 2) "too many links")))
 
 (defun nnmaildir--enoent-p (err)
   (error-has-type-p err 'file-missing))
diff --git a/lisp/ibuffer.el b/lisp/ibuffer.el
index 6777d652c44..04cc631ba6f 100644
--- a/lisp/ibuffer.el
+++ b/lisp/ibuffer.el
@@ -1131,7 +1131,7 @@ a new window in the current frame, splitting vertically."
 			       (and (stringp msg)
 				    ;; This definitely falls in the
 				    ;; ghetto hack category...
-				    (not (string-match-p "too small" msg)))))
+                                    (not (string-search "too small" msg)))))
 			 (signal err)
 		       (enlarge-window 3))))))
 	      (select-window (next-window))
diff --git a/test/lisp/vc/vc-tests/vc-tests.el b/test/lisp/vc/vc-tests/vc-tests.el
index 737ee09415e..a64bee00de2 100644
--- a/test/lisp/vc/vc-tests/vc-tests.el
+++ b/test/lisp/vc/vc-tests/vc-tests.el
@@ -236,7 +236,7 @@ For backends which don't support it, `vc-not-supported' is signaled."
 (defmacro vc-test--run-maybe-unsupported-function (func &rest args)
   "Run FUNC with ARGS as arguments.
 Catch the `vc-not-supported' error."
-  `(condition-case err
+  `(condition-case nil
        (funcall ,func ,@args)
      (vc-not-supported 'vc-not-supported)))