--- orig/user.lisp
+++ mod/user.lisp
@@ -98,7 +98,9 @@
 		 (car window-list)
 	       ;; Otherwise, focus the next one in the list.
 	       (cadr wins)))
-    (frame-raise-window screen (window-frame screen nw) nw)))
+    ;; If there are no windows in the frame, there is no window to focus.
+    (when nw
+      (frame-raise-window screen (window-frame screen nw) nw))))
 
 (defun delete-current-window (screen)
   "Send a delete event to the current window."
@@ -199,7 +201,9 @@
       ;; update the current frame and sync it's windows
       (setf (screen-current-frame screen) l)
       (sync-frame-windows screen l)
-      (frame-raise-window screen l (frame-window (frame-data screen l))))))
+      (let ((window (frame-window (frame-data screen l))))
+	(when window
+	  (frame-raise-window screen l window))))))
 
 (defun focus-frame-sibling (screen)
   (let* ((sib (sibling (screen-frame-tree screen)