diff --git a/lib/init.scm b/lib/init.scm
index 62d044ec..c8a807e7 100644
--- a/lib/init.scm
+++ b/lib/init.scm
@@ -525,6 +525,8 @@
 
 ;; I/O utils
 
+(define (port? x) (or (input-port? x) (output-port? x)))
+
 (define (char-ready? . o)
   (not (eof-object? (peek-char (if (pair? o) (car o) (current-input-port))))))