diff --git a/.changeset/fluffy-fans-watch.md b/.changeset/fluffy-fans-watch.md
new file mode 100644
index 000000000000..30c0a3723451
--- /dev/null
+++ b/.changeset/fluffy-fans-watch.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Only serialize data once body is rendered
diff --git a/packages/kit/src/runtime/server/page.js b/packages/kit/src/runtime/server/page.js
index e832e49b032f..89c709dc91be 100644
--- a/packages/kit/src/runtime/server/page.js
+++ b/packages/kit/src/runtime/server/page.js
@@ -26,8 +26,8 @@ async function get_response({ request, options, $session, route, status = 200, e
 		throw new Error(`Failed to serialize session data: ${error.message}`);
 	});
 
-	/** @type {Array<{ url: string, payload: string }>} */
-	const serialized_data = [];
+	/** @type {Array<{ url: string, response: Response }>} */
+	const inline_data = [];
 
 	const match = route && route.pattern.exec(request.path);
 	const params = route && route.params(match);
@@ -126,24 +126,11 @@ async function get_response({ request, options, $session, route, status = 200, e
 		}
 
 		if (response) {
-			const clone = response.clone();
-
-			/** @type {import('types.internal').Headers} */
-			const headers = {};
-			clone.headers.forEach((value, key) => {
-				if (key !== 'etag') headers[key] = value;
+			inline_data.push({
+				url,
+				response: response.clone()
 			});
 
-			const payload = JSON.stringify({
-				status: clone.status,
-				statusText: clone.statusText,
-				headers,
-				body: await clone.text() // TODO handle binary data
-			});
-
-			// TODO i guess we need to sanitize/escape this... somehow?
-			serialized_data.push({ url, payload });
-
 			return response;
 		}
 
@@ -353,14 +340,27 @@ async function get_response({ request, options, $session, route, status = 200, e
 		init
 	].join('\n\n');
 
-	const body = options.amp
-		? rendered.html
-		: `${rendered.html}
+	let body = rendered.html;
+
+	if (!options.amp) {
+		for (const { url, response } of inline_data) {
+			/** @type {import('types.internal').Headers} */
+			const headers = {};
+			response.headers.forEach((value, key) => {
+				if (key !== 'etag') headers[key] = value;
+			});
 
-			${serialized_data
-				.map(({ url, payload }) => `<script type="svelte-data" url="${url}">${payload}</script>`)
-				.join('\n\n\t\t\t')}
-		`.replace(/^\t{2}/gm, '');
+			const payload = JSON.stringify({
+				status: response.status,
+				statusText: response.statusText,
+				headers,
+				body: await response.text() // TODO handle binary data
+			});
+
+			// TODO i guess we need to sanitize/escape this... somehow?
+			body += `\n\n\t<script type="svelte-data" url="${url}">${payload}</script>`;
+		}
+	}
 
 	/** @type {import('types.internal').Headers} */
 	const headers = {