diff --git a/repl/src/pianoroll.mjs b/repl/src/pianoroll.mjs
index 3169caf0..a7a385ee 100644
--- a/repl/src/pianoroll.mjs
+++ b/repl/src/pianoroll.mjs
@@ -15,6 +15,7 @@ Pattern.prototype.pianoroll = function ({
   this.draw(
     (ctx, events, t) => {
       ctx.fillStyle = background;
+      ctx.clearRect(0, 0, w, h);
       ctx.fillRect(0, 0, w, h);
       events.forEach((event) => {
         const isActive = event.whole.begin <= t && event.whole.end >= t;