diff --git a/editor/editor.lisp b/editor/editor.lisp
index ba6a2cd..a871733 100644
--- a/editor/editor.lisp
+++ b/editor/editor.lisp
@@ -808,11 +808,14 @@ Additionally ensures correct line numbers on the way, as a bonus."
 (defun csi-handler ()
   (loop :for buffer := '() :then (append buffer (list (read-char *eio*)))
         :for found := (assoc buffer *csi-sequences* :test #'equalp)
-        :when (or found (not (zerop (some
-                                     (lambda (c)
-                                       (search buffer (car c)))
-                                     *csi-sequences*))))
-          :return (cadr found)))
+        :for match-point := (some
+                             (lambda (c)
+                               (search buffer (car c)))
+                             *csi-sequences*)
+        :when (or found (null match-point)
+                  (and (numberp match-point)
+                       (not (zerop match-point))))
+          :return (or (cadr found) :unknown)))
 
 (defun esc (key)
   (when (numberp key)