diff --git a/emacs/notmuch-lib.el b/emacs/notmuch-lib.el
index 61107e38..2c8de328 100644
--- a/emacs/notmuch-lib.el
+++ b/emacs/notmuch-lib.el
@@ -534,14 +534,10 @@ This replaces spaces, percents, and double quotes in STR with
       (setq pred (cddr pred)))
     (cdr xplist)))
 
-(defun notmuch-split-content-type (content-type)
-  "Split content/type into 'content' and 'type'."
-  (split-string content-type "/"))
-
 (defun notmuch-match-content-type (t1 t2)
   "Return t if t1 and t2 are matching content types, taking wildcards into account."
-  (let ((st1 (notmuch-split-content-type t1))
-	(st2 (notmuch-split-content-type t2)))
+  (let ((st1 (split-string t1 "/"))
+	(st2 (split-string t2 "/")))
     (if (or (string= (cadr st1) "*")
 	    (string= (cadr st2) "*"))
 	;; Comparison of content types should be case insensitive.
diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 14250d34..09cdeaaa 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -573,12 +573,13 @@ message at DEPTH in the current thread."
       ;; alternative (even if we can't render it).
       (push (list content-id msg part) notmuch-show--cids)))
   ;; Recurse on sub-parts
-  (let ((ctype (notmuch-split-content-type
-		(downcase (plist-get part :content-type)))))
-    (cond ((equal (car ctype) "multipart")
+  (pcase-let ((`(,content ,type)
+	       (split-string (downcase (plist-get part :content-type)) "/")))
+    (cond ((equal content "multipart")
 	   (mapc (apply-partially #'notmuch-show--register-cids msg)
 		 (plist-get part :content)))
-	  ((equal ctype '("message" "rfc822"))
+	  ((and (equal content "message")
+		(equal type "rfc822"))
 	   (notmuch-show--register-cids
 	    msg
 	    (car (plist-get (car (plist-get part :content)) :body)))))))
@@ -851,10 +852,9 @@ will return nil if the CID is unknown or cannot be retrieved."
 	      (push func result)))
 	  ;; Reverse order of prefrence.
 	  (list (intern (concat "notmuch-show-insert-part-*/*"))
-		(intern (concat
-			 "notmuch-show-insert-part-"
-			 (car (notmuch-split-content-type content-type))
-			 "/*"))
+		(intern (concat "notmuch-show-insert-part-"
+				(car (split-string content-type "/"))
+				"/*"))
 		(intern (concat "notmuch-show-insert-part-" content-type))))
     result))