diff --git a/design/models/0007-kernel-extensions.md b/design/models/0007-kernel-extensions.md
index 54db9e6..b1e51b9 100644
--- a/design/models/0007-kernel-extensions.md
+++ b/design/models/0007-kernel-extensions.md
@@ -77,7 +77,7 @@ moving average over a stream of float values, window size 3":
         (app print (app /
           (app sum_window_step s n 0 0.0)
           (app int_to_float n)))
-        unit)))
+        (do io/print_str ""))))
 
   (fn run_stream
     (type (fn-type
@@ -86,7 +86,7 @@ moving average over a stream of float values, window size 3":
     (params s n input)
     (body
       (match input
-        (case (pat-ctor FNil) unit)
+        (case (pat-ctor FNil) (do io/print_str ""))
         (case (pat-ctor FCons v rest)
           (let s_new (app Series.push s v)
             (seq (app emit_if_full s_new n)