diff --git a/packages/svelte/src/internal/client/render.js b/packages/svelte/src/internal/client/render.js
index dee595d25c..590ee46a46 100644
--- a/packages/svelte/src/internal/client/render.js
+++ b/packages/svelte/src/internal/client/render.js
@@ -158,6 +158,9 @@ export function hydrate(component, options) {
 		}, false);
 	} catch (error) {
 		if (error === HYDRATION_ERROR) {
+			// TODO it's possible for event listeners to have been added and
+			// not removed, e.g. with `<svelte:window>` or `<svelte:document>`
+
 			if (options.recover === false) {
 				e.hydration_failed();
 			}