diff --git a/networks.rkt b/networks.rkt
index f16c72c..07da868 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -1526,7 +1526,9 @@
 ;;; are 0.
 (define (compact-tbf tbf)
   (tbf/state
-   (hash-filter (tbf/state-w tbf) #:predicate (compose not zero?))
+   (for/hash ([(k v) (in-hash (tbf/state-w tbf))]
+              #:unless (zero? v))
+     (values k v))
    (tbf/state-θ tbf)))
 
 (module+ test