diff --git a/lisp/mouse.el b/lisp/mouse.el
index 30fe5e99ff..851da77ce0 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -488,14 +488,15 @@ context-menu-region
       `(menu-item "All"
                   ,(lambda (e) (interactive "e") (mark-thing-at-mouse e 'buffer))
                   :help "Mark the whole buffer for a subsequent cut/copy"))
-    (when (let* ((pos (posn-point (event-end click)))
-                 (char (when pos (char-after pos))))
-            (or (and char (eq (char-syntax char) ?\"))
-                (nth 3 (save-excursion (syntax-ppss pos)))))
-      (define-key-after submenu [mark-string]
-        `(menu-item "String"
-                    ,(lambda (e) (interactive "e") (mark-thing-at-mouse e 'string))
-                    :help "Mark the string at click for a subsequent cut/copy")))
+    (with-current-buffer (window-buffer)
+      (when (let* ((pos (posn-point (event-end click)))
+                   (char (when pos (char-after pos))))
+              (or (and char (eq (char-syntax char) ?\"))
+                  (nth 3 (save-excursion (syntax-ppss pos)))))
+        (define-key-after submenu [mark-string]
+          `(menu-item "String"
+                      ,(lambda (e) (interactive "e") (mark-thing-at-mouse e 'string))
+                      :help "Mark the string at click for a subsequent cut/copy"))))
     (define-key-after submenu [mark-line]
       `(menu-item "Line"
                   ,(lambda (e) (interactive "e") (mark-thing-at-mouse e 'line))
diff --git a/lisp/progmodes/prog-mode.el b/lisp/progmodes/prog-mode.el
index 30b6edf0d9..bf1f619858 100644
--- a/lisp/progmodes/prog-mode.el
+++ b/lisp/progmodes/prog-mode.el
@@ -93,7 +93,9 @@ prog-context-menu
     'mark-whole-buffer)
 
   ;; Include text-mode select menu only in strings and comments.
-  (when (nth 8 (save-excursion (syntax-ppss (posn-point (event-end click)))))
+  (when (nth 8 (save-excursion
+                 (with-current-buffer (window-buffer)
+                   (syntax-ppss (posn-point (event-end click))))))
     (text-mode-context-menu menu click))
 
   menu)