diff --git a/embddr/vcd.scm b/embddr/vcd.scm
index b4ffabc..df39352 100644
--- a/embddr/vcd.scm
+++ b/embddr/vcd.scm
@@ -258,7 +258,7 @@
 
                            ;; Update register values list
                            (let ((sigs (hash-table-ref/default tags+signals-ht tag #f)))
-                             (unless (null? sigs)
+                             (when sigs
                                (for-each
                                 (lambda (sig)
                                   (signal-add!