diff --git a/.changeset/hydrated-boundary-reset.md b/.changeset/hydrated-boundary-reset.md
new file mode 100644
index 0000000000..799a57fd9b
--- /dev/null
+++ b/.changeset/hydrated-boundary-reset.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: call `onerror` and provide a working `reset` when hydrating a failed boundary
diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 0c0903ff52..4f655a3695 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -199,17 +199,68 @@ export class Boundary {
 	 */
 	#hydrate_failed_content(error) {
 		const failed = this.#props.failed;
+		const { reset, invoke_onerror } = this.#create_reset(error);
+
+		// `onerror` may mutate state, which is disallowed while hydrating
+		queue_micro_task(invoke_onerror);
+
 		if (!failed) return;
 
 		this.#failed_effect = branch(() => {
 			failed(
 				this.#anchor,
 				() => error,
-				() => () => {}
+				() => reset
 			);
 		});
 	}
 
+	/**
+	 * Creates the `reset` function for a failed boundary, along with a function
+	 * that invokes `onerror` with it (if provided)
+	 * @param {unknown} error
+	 * @returns {{ reset: () => void, invoke_onerror: () => void }}
+	 */
+	#create_reset(error) {
+		var did_reset = false;
+		var calling_on_error = false;
+
+		const reset = () => {
+			if (did_reset) {
+				w.svelte_boundary_reset_noop();
+				return;
+			}
+
+			did_reset = true;
+
+			if (calling_on_error) {
+				e.svelte_boundary_reset_onerror();
+			}
+
+			if (this.#failed_effect !== null) {
+				pause_effect(this.#failed_effect, () => {
+					this.#failed_effect = null;
+				});
+			}
+
+			this.#run(() => {
+				this.#render();
+			});
+		};
+
+		const invoke_onerror = () => {
+			try {
+				calling_on_error = true;
+				this.#props.onerror?.(error, reset);
+				calling_on_error = false;
+			} catch (err) {
+				invoke_error_boundary(err, this.#effect && this.#effect.parent);
+			}
+		};
+
+		return { reset, invoke_onerror };
+	}
+
 	#hydrate_pending_content() {
 		const pending = this.#props.pending;
 		if (!pending) return;
@@ -429,43 +480,13 @@ export class Boundary {
 			set_hydrate_node(skip_nodes());
 		}
 
-		var onerror = this.#props.onerror;
 		let failed = this.#props.failed;
-		var did_reset = false;
-		var calling_on_error = false;
-
-		const reset = () => {
-			if (did_reset) {
-				w.svelte_boundary_reset_noop();
-				return;
-			}
-
-			did_reset = true;
-
-			if (calling_on_error) {
-				e.svelte_boundary_reset_onerror();
-			}
-
-			if (this.#failed_effect !== null) {
-				pause_effect(this.#failed_effect, () => {
-					this.#failed_effect = null;
-				});
-			}
-
-			this.#run(() => {
-				this.#render();
-			});
-		};
 
 		/** @param {unknown} transformed_error */
 		const handle_error_result = (transformed_error) => {
-			try {
-				calling_on_error = true;
-				onerror?.(transformed_error, reset);
-				calling_on_error = false;
-			} catch (error) {
-				invoke_error_boundary(error, this.#effect && this.#effect.parent);
-			}
+			const { reset, invoke_onerror } = this.#create_reset(transformed_error);
+
+			invoke_onerror();
 
 			if (failed) {
 				this.#failed_effect = this.#run(() => {
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/_config.js
new file mode 100644
index 0000000000..f0aef7e92f
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/_config.js
@@ -0,0 +1,19 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['hydrate'],
+	ssrHtml: '<p>failed: error</p> <button>reset</button>',
+	transformError: () => 'error',
+
+	test({ assert, target, logs }) {
+		// `onerror` is called upon hydration with the deserialized error
+		assert.deepEqual(logs, ['onerror: error']);
+
+		const btn = target.querySelector('button');
+		btn?.click();
+		flushSync();
+
+		assert.htmlEqual(target.innerHTML, '<p>recovered</p> <button>reset</button>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/child.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/child.svelte
new file mode 100644
index 0000000000..e93c7bb0fa
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/child.svelte
@@ -0,0 +1,3 @@
+<script>
+	throw new Error('unlucky');
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/main.svelte
new file mode 100644
index 0000000000..e84198473b
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-1/main.svelte
@@ -0,0 +1,29 @@
+<script>
+	import Child from './child.svelte';
+
+	let recovered = $state(false);
+	let reset_fn = $state();
+</script>
+
+<svelte:boundary
+	onerror={(error, reset) => {
+		console.log(`onerror: ${error}`);
+		reset_fn = reset;
+	}}
+>
+	{#if recovered}
+		<p>recovered</p>
+	{:else}
+		<Child />
+	{/if}
+
+	{#snippet failed(error)}
+		<p>failed: {error}</p>
+	{/snippet}
+</svelte:boundary>
+
+<button
+	onclick={() => {
+		recovered = true;
+		reset_fn();
+	}}>reset</button>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/_config.js
new file mode 100644
index 0000000000..e5c52eb19c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/_config.js
@@ -0,0 +1,16 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['hydrate'],
+	ssrHtml: '<p>failed: error</p> <button>reset</button>',
+	transformError: () => 'error',
+
+	test({ assert, target }) {
+		const btn = target.querySelector('button');
+		btn?.click();
+		flushSync();
+
+		assert.htmlEqual(target.innerHTML, '<p>recovered</p>');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/child.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/child.svelte
new file mode 100644
index 0000000000..e93c7bb0fa
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/child.svelte
@@ -0,0 +1,3 @@
+<script>
+	throw new Error('unlucky');
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/main.svelte
new file mode 100644
index 0000000000..1642a94e7a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-hydrate-2/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	import Child from './child.svelte';
+
+	let recovered = $state(false);
+</script>
+
+<svelte:boundary>
+	{#if recovered}
+		<p>recovered</p>
+	{:else}
+		<Child />
+	{/if}
+
+	{#snippet failed(error, reset)}
+		<p>failed: {error}</p>
+		<button
+			onclick={() => {
+				recovered = true;
+				reset();
+			}}>reset</button>
+	{/snippet}
+</svelte:boundary>