diff --git a/pitfall/pitfall/page.rkt b/pitfall/pitfall/page.rkt
index c18918d9..bd61be2d 100644
--- a/pitfall/pitfall/page.rkt
+++ b/pitfall/pitfall/page.rkt
@@ -8,7 +8,10 @@
 
 (provide (all-defined-out))
 
-(define (current-page doc) (car (pdf-pages doc)))
+(define (current-page doc)
+  (match (pdf-pages doc)
+    [(? pair? ps) (car ps)]
+    [_ (raise-argument-error 'current-page "no pages in pdf" doc)]))
 
 (define (add-content doc data)
   (page-write (current-page doc) data))