diff --git a/gem300.rkt b/gem300.rkt
index 16e6657..8bb47aa 100644
--- a/gem300.rkt
+++ b/gem300.rkt
@@ -31,7 +31,8 @@
 
 (define (next-cmd)
   (define (iter depth)
-    (when (> depth 0)
+    (when (and (> depth 0)
+               (> (pipe-content-length document-buffer) 0))
       (let ()
         (displayln (read-line document-buffer))
         (iter (sub1 depth)))))