diff --git a/scsh/newports.scm b/scsh/newports.scm
index 85c2f8d..6c7b28e 100644
--- a/scsh/newports.scm
+++ b/scsh/newports.scm
@@ -811,8 +811,8 @@
     (for-each input-port/fdes-check-unlocked read-list)
     (for-each output-port/fdes-check-unlocked write-list)
 
-    (let ((any-read (any-input-ready read-list))
-	  (any-write (any-output-ready write-list)))
+    (let ((any-read (any-input-ready (filter input-port? read-list)))
+	  (any-write (any-output-ready (filter output-port? write-list))))
 
       (if (or (pair? any-read) (pair? any-write))
 	  (begin