diff --git a/packages/client/src/components/MkWindow.vue b/packages/client/src/components/MkWindow.vue
index 758d4d47b6..0ab4382632 100644
--- a/packages/client/src/components/MkWindow.vue
+++ b/packages/client/src/components/MkWindow.vue
@@ -221,6 +221,8 @@ function onHeaderMousedown(evt: MouseEvent) {
 // 上ハンドル掴み時
 function onTopHandleMousedown(evt) {
 	const main = rootEl;
+	// どういうわけかnullになることがある
+	if (main == null) return;
 
 	const base = evt.clientY;
 	const height = parseInt(getComputedStyle(main, '').height, 10);
@@ -247,6 +249,7 @@ function onTopHandleMousedown(evt) {
 // 右ハンドル掴み時
 function onRightHandleMousedown(evt) {
 	const main = rootEl;
+	if (main == null) return;
 
 	const base = evt.clientX;
 	const width = parseInt(getComputedStyle(main, '').width, 10);
@@ -271,6 +274,7 @@ function onRightHandleMousedown(evt) {
 // 下ハンドル掴み時
 function onBottomHandleMousedown(evt) {
 	const main = rootEl;
+	if (main == null) return;
 
 	const base = evt.clientY;
 	const height = parseInt(getComputedStyle(main, '').height, 10);
@@ -295,6 +299,7 @@ function onBottomHandleMousedown(evt) {
 // 左ハンドル掴み時
 function onLeftHandleMousedown(evt) {
 	const main = rootEl;
+	if (main == null) return;
 
 	const base = evt.clientX;
 	const width = parseInt(getComputedStyle(main, '').width, 10);
@@ -366,6 +371,8 @@ function applyTransformLeft(left) {
 
 function onBrowserResize() {
 	const main = rootEl;
+	if (main == null) return;
+
 	const position = main.getBoundingClientRect();
 	const browserWidth = window.innerWidth;
 	const browserHeight = window.innerHeight;