diff --git a/.changeset/sour-jars-sniff.md b/.changeset/sour-jars-sniff.md
new file mode 100644
index 000000000000..e8e59a029276
--- /dev/null
+++ b/.changeset/sour-jars-sniff.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: update untracked writes for `BLOCK_EFFECT`s too
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/A.svelte b/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/A.svelte
new file mode 100644
index 000000000000..c4b6f2e3a087
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/A.svelte
@@ -0,0 +1,10 @@
+<script>
+	let {config, value = $bindable()} = $props();
+
+	$effect.pre(() => {
+		config;
+		value = {}
+	});
+</script>
+
+a
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/B.svelte b/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/B.svelte
new file mode 100644
index 000000000000..17bc76f775de
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/B.svelte
@@ -0,0 +1,10 @@
+<script>
+	let {config, value = $bindable()} = $props();
+
+	$effect.pre(() => {
+		config;
+		value = {}
+	});
+</script>
+
+b
\ No newline at end of file
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/_config.js b/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/_config.js
new file mode 100644
index 000000000000..c2f95c88827a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/_config.js
@@ -0,0 +1,14 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: '<button></button> a',
+	async test({ assert, target }) {
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+
+		assert.htmlEqual(target.innerHTML, `<button></button> b`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/main.svelte b/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/main.svelte
new file mode 100644
index 000000000000..a898b909e131
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	import A from "./A.svelte";
+	import B from "./B.svelte";
+	
+	let schema = $state("any");
+	let value = $state({});
+
+	let config = $derived.by(() => {
+		value;
+		return schema;
+	});
+
+	let Thing = $derived.by(() => {
+		return config === "any" ? A : B;
+	});
+</script>
+
+<button onclick={()=>{
+	schema = "one";
+}}></button>
+
+<Thing {config} bind:value/>
\ No newline at end of file