diff --git a/collects/redex/private/traces.rkt b/collects/redex/private/traces.rkt
index 5906c2445c..35f71de5af 100644
--- a/collects/redex/private/traces.rkt
+++ b/collects/redex/private/traces.rkt
@@ -291,7 +291,10 @@
                       (init-value (initial-font-size))
                       (max-value 127)
                       (parent bottom-panel)
-                      (callback (lambda (slider evt) (set-font-size (send slider get-value))))))
+                      (callback (lambda (slider evt) 
+                                  (send graph-pb begin-edit-sequence)
+                                  (set-font-size (send slider get-value))
+                                  (send graph-pb end-edit-sequence)))))
   (define lower-panel (instantiate horizontal-panel% ()
                         (parent bottom-panel)
                         (stretchable-height #f)))