diff --git a/src/editor/Editor.ts b/src/editor/Editor.ts
index 0285d7c6..b145dfa9 100644
--- a/src/editor/Editor.ts
+++ b/src/editor/Editor.ts
@@ -364,7 +364,7 @@ export class Editor implements PlayHost {
       const playing = this.play.machineStates(assetId);
       return playing.length > 0 ? playing : this.editorRun.machineStates(assetId);
     };
-    // Only one of the two ever runs a given asset: playing stops the editor run (see `EditorRun.tick`).
+    // Only one of the two ever runs a given asset: playing stops the editor run (see `EditorRun.modeChanged`).
     this.inspector.liveVariables = (assetId) =>
       this.play.liveVariables(assetId) ?? this.editorRun.liveVariables(assetId);
     this.variablesEditor.liveVariables = this.inspector.liveVariables;
@@ -560,7 +560,7 @@ export class Editor implements PlayHost {
       this.valueTargets.clear();
       this.showTab('scene');
     });
-    state.on('mode', () => this.editorRun.invalidate());
+    state.on('mode', () => this.editorRun.modeChanged());
     state.on('pick', () => this.followPick());
   }
 
diff --git a/src/editor/EditorRun.ts b/src/editor/EditorRun.ts
index fadd0d91..42e85873 100644
--- a/src/editor/EditorRun.ts
+++ b/src/editor/EditorRun.ts
@@ -41,6 +41,15 @@ export class EditorRun {
     if (!this.writing) this.stale = true;
   }
 
+  /**
+   * Playing starts: the run ends at once, not on the next frame. The game's `On start` runs in the
+   * same click, and stopping the run's sounds a frame later would take its music along.
+   */
+  modeChanged(): void {
+    if (this.state.mode !== 'edit') this.stop();
+    this.invalidate();
+  }
+
   /** `step` is what the global clock moved this frame – already scaled and capped. */
   tick(step: number): void {
     if (this.state.mode !== 'edit') {
diff --git a/tests/editor/editor-run.test.ts b/tests/editor/editor-run.test.ts
index 62944c3c..76e9e0ad 100644
--- a/tests/editor/editor-run.test.ts
+++ b/tests/editor/editor-run.test.ts
@@ -178,6 +178,24 @@ describe('the run-in-editor switch', () => {
     expect(f.boxX()).toBe(0);
   });
 
+  it('ends the moment playing starts, before the game’s On start, not a frame later', () => {
+    const f = scene();
+    f.state.on('mode', () => f.run.modeChanged());
+    f.state.execute(new SetOverrideCommand(f.sceneId, f.logic, 'runInEditor', true));
+    f.frame(0.1);
+    expect(f.run.debugInfo().running).toBe(true);
+
+    // The game is built right after `enterPlay` in the same click; a run ended only by the next
+    // frame stopped every sound, the music its On start had just begun with them.
+    f.state.enterPlay();
+    expect(f.run.debugInfo().running).toBe(false);
+    expect(f.keyboard.world).toBeNull();
+
+    f.state.exitPlay();
+    f.frame(0.1);
+    expect(f.run.debugInfo().running).toBe(true);
+  });
+
   it('does not run a behavior whose scene is not the loaded one', () => {
     const f = scene();
     f.state.execute(new SetOverrideCommand(f.sceneId, f.logic, 'runInEditor', true));
diff --git a/tools/e2e/64-pattern.mjs b/tools/e2e/64-pattern.mjs
index 58429565..a943181a 100644
--- a/tools/e2e/64-pattern.mjs
+++ b/tools/e2e/64-pattern.mjs
@@ -510,6 +510,21 @@ export async function pattern(t) {
       edges: [edge('pt64-e3', 'pt64-start', 'exec', 'pt64-play', 'exec')],
     },
   });
+  // A behavior running in the editor ends when the game starts, and its sounds with it – but only
+  // its own: the pattern the game's `On start` plays in the same click has to live on.
+  const idle = await scaffoldBehavior(t, {
+    assetId: 'pt64-idle',
+    name: 'Idle 64',
+    boxId: 'pt64-idlebox',
+    logicId: 'pt64-idler',
+    y: LANES.sound + 200,
+    props: { enabled: true, runInEditor: true },
+    graph: { nodes: [node('pt64-idle-start', 'OnStart', 0, 0)], edges: [] },
+  });
+  await waitFor(
+    () => json('__gm.editorRun().running'),
+    (running) => running,
+  );
   const patterns = () => json('__gm.sound.playbacks()');
   await evaluate('__gm.sound.stopAll()');
   await play();
@@ -556,6 +571,7 @@ export async function pattern(t) {
     JSON.stringify({ once: once.map((g) => g.planned.length), gone, onceStats }),
   );
   const left = await rig.remove();
+  const idleLeft = await idle.remove();
 
   // 64m. The step takes back everything it made.
   await evaluate('__gm.sound.stopAll()');
@@ -571,7 +587,10 @@ export async function pattern(t) {
       `__gm.state.project.assets.filter((a) => a.id.startsWith('pt64') || a.type === 'pattern').length`,
     )) === 0 &&
       left.objects === 0 &&
-      left.assets === 0,
-    JSON.stringify(left),
+      left.assets === 0 &&
+      idleLeft.objects === 0 &&
+      idleLeft.assets === 0 &&
+      !(await json('__gm.editorRun().running')),
+    JSON.stringify({ left, idleLeft }),
   );
 }