From 4f41e816baa007fb6a4e31164da49576e87e342e Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 4 Feb 2026 13:07:46 -0500
Subject: [PATCH] fix: ensure infinite effect loops are cleared after flushing
 (#17601)

* failing effect-loop-infinite test

* fix
---
 .changeset/chatty-mammals-find.md                     |  5 +++++
 .../svelte/src/internal/client/reactivity/batch.js    |  3 ++-
 packages/svelte/tests/runtime-legacy/shared.ts        |  2 ++
 .../samples/effect-loop-infinite/_config.js           | 11 ++++++-----
 4 files changed, 15 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/chatty-mammals-find.md

diff --git a/.changeset/chatty-mammals-find.md b/.changeset/chatty-mammals-find.md
new file mode 100644
index 0000000000..373dc0059a
--- /dev/null
+++ b/.changeset/chatty-mammals-find.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure infinite effect loops are cleared after flushing
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index cef2df4716..9bf93c873f 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -647,8 +647,9 @@ function flush_effects() {
 			}
 		}
 	} finally {
-		is_flushing = false;
+		queued_root_effects = [];
 
+		is_flushing = false;
 		last_scheduled_effect = null;
 
 		if (DEV) {
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index 8c29a6ada2..c5317f822e 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -521,6 +521,8 @@ async function run_test_variant(
 						errors,
 						hydrate: hydrate_fn
 					});
+
+					flushSync();
 				}
 
 				if (config.runtime_error && !unhandled_rejection) {
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
index 57f60c2b44..44cf5b09e2 100644
--- a/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
@@ -11,11 +11,12 @@ export default test({
 	test({ assert, errors }) {
 		const [button] = document.querySelectorAll('button');
 
-		try {
+		assert.throws(() => {
 			flushSync(() => button.click());
-		} catch (e) {
-			assert.equal(errors.length, 1); // for whatever reason we can't get the name which should be 'updated at'
-			assert.ok(/** @type {Error} */ (e).message.startsWith('effect_update_depth_exceeded'));
-		}
+		}, /effect_update_depth_exceeded/);
+
+		assert.equal(errors.length, 1);
+
+		assert.doesNotThrow(flushSync);
 	}
 });