diff --git a/packages/svelte/src/internal/client/dom/blocks/key.js b/packages/svelte/src/internal/client/dom/blocks/key.js
index e70b81de15..3cadbb3345 100644
--- a/packages/svelte/src/internal/client/dom/blocks/key.js
+++ b/packages/svelte/src/internal/client/dom/blocks/key.js
@@ -22,7 +22,11 @@ export function key_block(anchor_node, get_key, render_fn) {
 	/** @type {import('#client').Effect} */
 	let effect;
 
-	/** @type {Set<import('#client').Effect>} */
+	/**
+	 * Every time `key` changes, we create a new effect. Old effects are
+	 * removed from this set when they have fully transitioned out
+	 * @type {Set<import('#client').Effect>}
+	 */
 	let effects = new Set();
 
 	const key_effect = render_effect(
diff --git a/packages/svelte/src/internal/client/dom/blocks/svelte-component.js b/packages/svelte/src/internal/client/dom/blocks/svelte-component.js
index 1ea6f7712b..e68df96330 100644
--- a/packages/svelte/src/internal/client/dom/blocks/svelte-component.js
+++ b/packages/svelte/src/internal/client/dom/blocks/svelte-component.js
@@ -23,7 +23,11 @@ export function component(anchor_node, get_component, render_fn) {
 	/** @type {import('#client').Effect} */
 	let effect;
 
-	/** @type {Set<import('#client').Effect>} */
+	/**
+	 * Every time `component` changes, we create a new effect. Old effects are
+	 * removed from this set when they have fully transitioned out
+	 * @type {Set<import('#client').Effect>}
+	 */
 	let effects = new Set();
 
 	const component_effect = render_effect(