diff --git a/.changeset/wild-chairs-build.md b/.changeset/wild-chairs-build.md
new file mode 100644
index 0000000000..494a3d70c5
--- /dev/null
+++ b/.changeset/wild-chairs-build.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+breaking: state mutations inside the template are no longer allowed
diff --git a/documentation/docs/98-reference/.generated/client-errors.md b/documentation/docs/98-reference/.generated/client-errors.md
index 4e7016b337..d6bd276de7 100644
--- a/documentation/docs/98-reference/.generated/client-errors.md
+++ b/documentation/docs/98-reference/.generated/client-errors.md
@@ -125,5 +125,5 @@ Reading state that was created inside the same derived is forbidden. Consider us
 ### state_unsafe_mutation
 
 ```
-Updating state inside a derived or logic block expression is forbidden. If the value should not be reactive, declare it without `$state`
+Updating state inside a derived or a template expression is forbidden. If the value should not be reactive, declare it without `$state`
 ```
diff --git a/packages/svelte/messages/client-errors/errors.md b/packages/svelte/messages/client-errors/errors.md
index 570a384d7c..954214cb81 100644
--- a/packages/svelte/messages/client-errors/errors.md
+++ b/packages/svelte/messages/client-errors/errors.md
@@ -82,4 +82,4 @@
 
 ## state_unsafe_mutation
 
-> Updating state inside a derived or logic block expression is forbidden. If the value should not be reactive, declare it without `$state`
+> Updating state inside a derived or a template expression is forbidden. If the value should not be reactive, declare it without `$state`
diff --git a/packages/svelte/src/internal/client/errors.js b/packages/svelte/src/internal/client/errors.js
index a0f33fb784..2a8f0e8914 100644
--- a/packages/svelte/src/internal/client/errors.js
+++ b/packages/svelte/src/internal/client/errors.js
@@ -343,12 +343,12 @@ export function state_unsafe_local_read() {
 }
 
 /**
- * Updating state inside a derived or logic block expression is forbidden. If the value should not be reactive, declare it without `$state`
+ * Updating state inside a derived or a template expression is forbidden. If the value should not be reactive, declare it without `$state`
  * @returns {never}
  */
 export function state_unsafe_mutation() {
 	if (DEV) {
-		const error = new Error(`state_unsafe_mutation\nUpdating state inside a derived or logic block expression is forbidden. If the value should not be reactive, declare it without \`$state\``);
+		const error = new Error(`state_unsafe_mutation\nUpdating state inside a derived or a template expression is forbidden. If the value should not be reactive, declare it without \`$state\``);
 
 		error.name = 'Svelte error';
 		throw error;
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index ba17b8d5aa..193c6df145 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -326,7 +326,7 @@ export function template_effect(fn) {
 			value: '{expression}'
 		});
 	}
-	return render_effect(fn);
+	return block(fn);
 }
 
 /**
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-template/_config.js b/packages/svelte/tests/runtime-runes/samples/side-effect-template/_config.js
new file mode 100644
index 0000000000..b17c83849f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-template/_config.js
@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	test({ assert, target }) {
+		const button = target.querySelector('button');
+
+		assert.throws(() => {
+			button?.click();
+			flushSync();
+		}, /state_unsafe_mutation/);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/side-effect-template/main.svelte b/packages/svelte/tests/runtime-runes/samples/side-effect-template/main.svelte
new file mode 100644
index 0000000000..0a53a08673
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/side-effect-template/main.svelte
@@ -0,0 +1,6 @@
+<script>
+	let items = $state([]);
+</script>
+
+<button onclick={() => items.push(3, 2, 1)}>Add</button>
+{JSON.stringify(items.sort())}
diff --git a/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after/main.svelte b/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after/main.svelte
index 5f8b19f4c7..e097c639f0 100644
--- a/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/store-unsubscribe-not-referenced-after/main.svelte
@@ -1,4 +1,5 @@
 <script>
+	import { untrack } from "svelte";
 	import { writable, derived } from "svelte/store";
 
 	const obj = writable({ a: 1 });
@@ -7,7 +8,9 @@
 
 	function watch (prop) {
 		return derived(obj, (o) => {
-			count++;
+			untrack(() => {
+				count++;
+			});
 			return o[prop];
 		});
 	}