diff --git a/.changeset/small-singers-smell.md b/.changeset/small-singers-smell.md
new file mode 100644
index 00000000000..ee7a8d06ec7
--- /dev/null
+++ b/.changeset/small-singers-smell.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': patch
+---
+
+Fixes HTML validity in sidebar groups by ensuring `<summary>` is the first child of `<details>`
diff --git a/packages/starlight/components/SidebarSublist.astro b/packages/starlight/components/SidebarSublist.astro
index c83a2f632e6..f90d79d3f73 100644
--- a/packages/starlight/components/SidebarSublist.astro
+++ b/packages/starlight/components/SidebarSublist.astro
@@ -37,7 +37,6 @@ const { sublist, nested } = Astro.props;
 					<details
 						open={flattenSidebar(entry.entries).some((i) => i.isCurrent) || !entry.collapsed}
 					>
-						<SidebarRestorePoint />
 						<summary>
 							<span class="group-label">
 								<span class="large">{entry.label}</span>
@@ -51,6 +50,7 @@ const { sublist, nested } = Astro.props;
 							</span>
 							<Icon name="right-caret" class="caret" size="1.25rem" />
 						</summary>
+						<SidebarRestorePoint />
 						<Astro.self sublist={entry.entries} nested />
 					</details>
 				)}