diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e8add521..205c780c2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,11 @@
 
 -->
 
+## 12.89.2 (2021/08/24)
+
+### Bugfixes
+- カスタムCSSを有効にしているとエラーになる問題を修正
+
 ## 12.89.1 (2021/08/24)
 
 ### Improvements
diff --git a/src/server/web/boot.js b/src/server/web/boot.js
index 7a41ae255..a3a068566 100644
--- a/src/server/web/boot.js
+++ b/src/server/web/boot.js
@@ -109,7 +109,7 @@
 	if (customCss && customCss.length > 0) {
 		const style = document.createElement('style');
 		style.innerHTML = customCss;
-		head.appendChild(style);
+		document.head.appendChild(style);
 	}
 
 	// eslint-disable-next-line no-inner-declarations