diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5a76139..bbecef6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,5 +5,6 @@ All notable changes to the "cyezoi" extension will be documented in this file.
 ## v0.0.34
 
 - Fix grammar mistake
+- Fix undefined star
 
 Want to see the previous log? [Click here](https://github.com/CYEZOI/cyezoi-helper/commits/main/CHANGELOG.md)
diff --git a/src/extension.ts b/src/extension.ts
index b06f825..5b23671 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -192,7 +192,7 @@ export const activate = async (context: vscode.ExtensionContext) => {
 		pid = await ensureData(pid?.toString(), 'pid', 'problem ID', vscode.window.activeTextEditor?.document.fileName.match(/\d+/)?.[0]);
 		if (!pid) { return; }
 		try {
-			const lastState = await new cyezFetch({ path: `/d/problemset/p/${pid}` }).start().then(response => response.json.psdoc.star);
+			const lastState = await new cyezFetch({ path: `/d/problemset/p/${pid}` }).start().then(response => response.json.psdoc?.star);
 			await new cyezFetch({
 				path: `/d/problemset/p/${pid}`,
 				body: {
diff --git a/src/treeView/pTree.ts b/src/treeView/pTree.ts
index ecf4c1f..b64e342 100644
--- a/src/treeView/pTree.ts
+++ b/src/treeView/pTree.ts
@@ -33,7 +33,7 @@ export default class extends treeView<Problem | ProblemRecord> {
 
 export class Problem extends vscode.TreeItem {
     constructor(pdoc: utils.ProblemDoc, psdoc: utils.ProblemStatusDoc, tid?: string) {
-        super((psdoc && psdoc.star ? "★ " : "") + 'P' + pdoc.docId, (psdoc && psdoc.status ? vscode.TreeItemCollapsibleState.Collapsed : vscode.TreeItemCollapsibleState.None));
+        super((psdoc?.star ? "★ " : "") + 'P' + pdoc.docId, (psdoc && psdoc.status ? vscode.TreeItemCollapsibleState.Collapsed : vscode.TreeItemCollapsibleState.None));
         this.id = (tid ? tid + '-' : '') + pdoc.docId;
         this.contextValue = 'problem';
         this.description = pdoc.title;