diff --git a/.changeset/dirty-teachers-know.md b/.changeset/dirty-teachers-know.md
new file mode 100644
index 000000000000..951117ffff1a
--- /dev/null
+++ b/.changeset/dirty-teachers-know.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes a potential null access in the clientside router
diff --git a/packages/astro/src/transitions/router.ts b/packages/astro/src/transitions/router.ts
index 2be12895e53f..cb5476a7a588 100644
--- a/packages/astro/src/transitions/router.ts
+++ b/packages/astro/src/transitions/router.ts
@@ -636,7 +636,7 @@ if (inBrowser) {
 				'scroll',
 				() => {
 					if (intervalId !== undefined) return;
-					(lastIndex = history.state.index), (lastY = scrollY), (lastX = scrollX);
+					(lastIndex = history.state?.index), (lastY = scrollY), (lastX = scrollX);
 					intervalId = window.setInterval(scrollInterval, 50);
 				},
 				{ passive: true },