diff --git a/packages/frontend/core/src/components/pure/ai-island/index.tsx b/packages/frontend/core/src/components/pure/ai-island/index.tsx
index e5517f8ef255a..485a543e69eb2 100644
--- a/packages/frontend/core/src/components/pure/ai-island/index.tsx
+++ b/packages/frontend/core/src/components/pure/ai-island/index.tsx
@@ -13,7 +13,11 @@ import {
   borderAngle3,
 } from './styles.css';
 
-if (typeof window !== 'undefined' && window.CSS) {
+if (
+  typeof window !== 'undefined' &&
+  window.CSS &&
+  window.CSS.registerProperty
+) {
   const getName = (nameWithVar: string) => nameWithVar.slice(4, -1);
   const registerAngle = (varName: string, initialValue: number) => {
     window.CSS.registerProperty({
diff --git a/packages/frontend/core/src/modules/peek-view/view/modal-container.tsx b/packages/frontend/core/src/modules/peek-view/view/modal-container.tsx
index d8d4b063a8a65..ec036d89e8f49 100644
--- a/packages/frontend/core/src/modules/peek-view/view/modal-container.tsx
+++ b/packages/frontend/core/src/modules/peek-view/view/modal-container.tsx
@@ -103,11 +103,15 @@ export const PeekViewModalContainer = forwardRef<
 ) {
   const [vtOpen, setVtOpen] = useState(open);
   useEffect(() => {
-    document.startViewTransition(() => {
-      flushSync(() => {
-        setVtOpen(open);
+    if (document.startViewTransition) {
+      document.startViewTransition(() => {
+        flushSync(() => {
+          setVtOpen(open);
+        });
       });
-    });
+    } else {
+      setVtOpen(open);
+    }
   }, [open]);
 
   useEffect(() => {