diff --git a/src/lib/components/chat/Messages/Markdown/KatexRenderer.svelte b/src/lib/components/chat/Messages/Markdown/KatexRenderer.svelte
index cfe7d8b1f7..63d2119cfd 100644
--- a/src/lib/components/chat/Messages/Markdown/KatexRenderer.svelte
+++ b/src/lib/components/chat/Messages/Markdown/KatexRenderer.svelte
@@ -38,7 +38,11 @@
 		try {
 			renderedHTML = renderToString(content, { displayMode, throwOnError: false });
 		} catch {
-			renderedHTML = content;
+			// throwOnError only suppresses ParseError; RangeError on deep nesting escapes, so escape the fallback (never {@html} raw source)
+			renderedHTML = content
+				.replaceAll('&', '&')
+				.replaceAll('<', '&lt;')
+				.replaceAll('>', '&gt;');
 		}
 	}
 </script>