diff --git a/lisp/emacs-lisp/lisp-mode.el b/lisp/emacs-lisp/lisp-mode.el
index 268992295bf..daf49670894 100644
--- a/lisp/emacs-lisp/lisp-mode.el
+++ b/lisp/emacs-lisp/lisp-mode.el
@@ -178,13 +178,16 @@
 
 (defun lisp--match-hidden-arg (limit)
   (let ((res nil))
+    (forward-line 0)
     (while
-        (let ((ppss (parse-partial-sexp (line-beginning-position)
+        (let ((ppss (parse-partial-sexp (point)
                                         (line-end-position)
                                         -1)))
           (skip-syntax-forward " )")
           (if (or (>= (car ppss) 0)
-                  (looking-at ";\\|$"))
+                  (eolp)
+                  (looking-at ";")
+                  (nth 8 (syntax-ppss))) ;Within a string or comment.
               (progn
                 (forward-line 1)
                 (< (point) limit))
diff --git a/test/lisp/custom-tests.el b/test/lisp/custom-tests.el
index a1451cf0ce6..7691f167738 100644
--- a/test/lisp/custom-tests.el
+++ b/test/lisp/custom-tests.el
@@ -156,4 +156,13 @@
   (load custom-test-admin-cus-test)
   (should (null (cus-test-opts t))))
 
+(ert-deftest custom-test-enable-theme-keeps-settings ()
+  "Test that enabling a theme doesn't change its settings."
+  (let* ((custom-theme-load-path `(,(ert-resource-directory)))
+         settings)
+    (load-theme 'custom--test 'no-confirm 'no-enable)
+    (setq settings (get 'custom--test 'theme-settings))
+    (enable-theme 'custom--test)
+    (should (equal settings (get 'custom--test 'theme-settings)))))
+
 ;;; custom-tests.el ends here