diff --git a/collects/2htdp/private/img-err.rkt b/collects/2htdp/private/img-err.rkt
index 06aa436046..62f13518dc 100644
--- a/collects/2htdp/private/img-err.rkt
+++ b/collects/2htdp/private/img-err.rkt
@@ -11,6 +11,7 @@
          pen-cap?
          pen-join?
          real-valued-posn?
+         step-count?
          check-mode/color-combination)
 
 (require htdp/error