diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index e51fab23f9..e6490763d2 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -216,6 +216,8 @@ export class Batch {
 		flush_queued_root_effects();
 
 		if (current_batch !== this) {
+			// this can happen if a `flushSync` occurred during `flush_queued_root_effects`,
+			// which is permitted in legacy mode despite being a terrible idea
 			return;
 		}