diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index 60abf54b2bb..2f213dab8b1 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -810,7 +810,8 @@ is inside the directory hierarchy of the project's root."
          (predicate
           (lambda (buffer)
             ;; BUFFER is an entry (BUF-NAME . BUF-OBJ) of Vbuffer_alist.
-            (and (not (eq (cdr buffer) current-buffer))
+            (and (cdr buffer)
+                 (not (eq (cdr buffer) current-buffer))
                  (when-let ((file (buffer-local-value 'default-directory
                                                       (cdr buffer))))
                    (file-in-directory-p file root))))))