diff --git a/ui/analyse/src/study/gamebook/gamebookPlayCtrl.ts b/ui/analyse/src/study/gamebook/gamebookPlayCtrl.ts
index d91f80fd7afb8..20193409b3244 100644
--- a/ui/analyse/src/study/gamebook/gamebookPlayCtrl.ts
+++ b/ui/analyse/src/study/gamebook/gamebookPlayCtrl.ts
@@ -1,5 +1,5 @@
 import AnalyseCtrl from '../../ctrl';
-import { path as treePath, ops as treeOps } from 'tree';
+import { path as treePath } from 'tree';
 import { makeShapesFromUci } from '../../autoShape';
 
 export type Feedback = 'play' | 'good' | 'bad' | 'end';
@@ -21,13 +21,6 @@ export default class GamebookPlayCtrl {
     readonly trans: Trans,
     readonly redraw: () => void,
   ) {
-    // ensure all original nodes have a gamebook entry,
-    // so we can differentiate original nodes from user-made ones
-    treeOps.updateAll(root.tree.root, n => {
-      n.gamebook = n.gamebook || {};
-      if (n.shapes) n.gamebook.shapes = n.shapes.slice(0);
-    });
-
     this.makeState();
   }
 
@@ -54,7 +47,7 @@ export default class GamebookPlayCtrl {
     } else {
       state.feedback = 'bad';
       if (!state.comment) {
-        state.comment = parNode.children[0].gamebook!.deviation;
+        state.comment = parNode.children[0].gamebook?.deviation;
       }
     }
     this.state = state as State;
diff --git a/ui/analyse/src/study/studyCtrl.ts b/ui/analyse/src/study/studyCtrl.ts
index 0e3b2ed5f98d8..086d34cf39cf0 100644
--- a/ui/analyse/src/study/studyCtrl.ts
+++ b/ui/analyse/src/study/studyCtrl.ts
@@ -15,7 +15,7 @@ import { StudyShare } from './studyShare';
 import { TagsForm } from './studyTags';
 import ServerEval from './serverEval';
 import * as xhr from './studyXhr';
-import { path as treePath } from 'tree';
+import { path as treePath, ops as treeOps } from 'tree';
 import {
   StudyVm,
   Tab,
@@ -404,6 +404,12 @@ export default class StudyCtrl {
 
   instanciateGamebookPlay = () => {
     if (!this.isGamebookPlay()) return (this.gamebookPlay = undefined);
+    // ensure all original nodes have a gamebook entry,
+    // so we can differentiate original nodes from user-made ones
+    treeOps.updateAll(this.ctrl.tree.root, n => {
+      n.gamebook = n.gamebook || {};
+      if (n.shapes) n.gamebook.shapes = n.shapes.slice(0);
+    });
     if (this.gamebookPlay?.chapterId === this.vm.chapterId) return;
     this.gamebookPlay = new GamebookPlayCtrl(this.ctrl, this.vm.chapterId, this.ctrl.trans, this.redraw);
     this.vm.mode.sticky = false;