diff --git a/.changeset/breezy-teachers-clean.md b/.changeset/breezy-teachers-clean.md
new file mode 100644
index 000000000..f6c841530
--- /dev/null
+++ b/.changeset/breezy-teachers-clean.md
@@ -0,0 +1,7 @@
+---
+'astro': patch
+---
+
+Final perf fix from 1.3.0 regression
+
+A regression in rendering perf happened in 1.3.0. This is the final fix for the underlying issue.
diff --git a/packages/astro/src/runtime/server/render/any.ts b/packages/astro/src/runtime/server/render/any.ts
index f4ffc21af..1a19ef519 100644
--- a/packages/astro/src/runtime/server/render/any.ts
+++ b/packages/astro/src/runtime/server/render/any.ts
@@ -1,4 +1,4 @@
-import { escapeHTML, HTMLString, markHTMLString } from '../escape.js';
+import { escapeHTML, isHTMLString, markHTMLString } from '../escape.js';
 import { AstroComponent, renderAstroComponent } from './astro.js';
 import { SlotString } from './slot.js';
 
@@ -9,7 +9,7 @@ export async function* renderChild(child: any): AsyncIterable<any> {
 			yield* child.instructions;
 		}
 		yield child;
-	} else if (child instanceof HTMLString) {
+	} else if (isHTMLString(child)) {
 		yield child;
 	} else if (Array.isArray(child)) {
 		for (const value of child) {