diff --git a/.changeset/reactive-has-own.md b/.changeset/reactive-has-own.md
new file mode 100644
index 0000000000..2ec5d27cee
--- /dev/null
+++ b/.changeset/reactive-has-own.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make Object.hasOwn reactive for state proxy ownership changes
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 91d82f8903..d7e8c98896 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -204,16 +204,21 @@ export function proxy(value) {
 		},
 
 		getOwnPropertyDescriptor(target, prop) {
+			this.has?.(target, prop);
+
 			var descriptor = Reflect.getOwnPropertyDescriptor(target, prop);
+			var s = sources.get(prop);
 
-			if (descriptor && 'value' in descriptor) {
-				var s = sources.get(prop);
-				if (s) descriptor.value = get(s);
-			} else if (descriptor === undefined) {
-				var source = sources.get(prop);
-				var value = source?.v;
+			if (s !== undefined) {
+				var value = get(s);
+
+				if (value === UNINITIALIZED) {
+					return undefined;
+				}
 
-				if (source !== undefined && value !== UNINITIALIZED) {
+				if (descriptor && 'value' in descriptor) {
+					descriptor.value = value;
+				} else {
 					return {
 						enumerable: true,
 						configurable: true,
diff --git a/packages/svelte/tests/runtime-runes/samples/object-has-own-reactive/_config.js b/packages/svelte/tests/runtime-runes/samples/object-has-own-reactive/_config.js
new file mode 100644
index 0000000000..17344b343d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/object-has-own-reactive/_config.js
@@ -0,0 +1,24 @@
+import { test } from '../../test';
+import { tick } from 'svelte';
+
+export default test({
+	html: `<button>add y</button><button>delete y</button><p>false</p>`,
+
+	async test({ assert, target }) {
+		const [add, remove] = target.querySelectorAll('button');
+
+		add.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>add y</button><button>delete y</button><p>true</p>`
+		);
+
+		remove.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			`<button>add y</button><button>delete y</button><p>false</p>`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/object-has-own-reactive/main.svelte b/packages/svelte/tests/runtime-runes/samples/object-has-own-reactive/main.svelte
new file mode 100644
index 0000000000..bd0773ae83
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/object-has-own-reactive/main.svelte
@@ -0,0 +1,7 @@
+<script>
+	let state = $state({});
+</script>
+
+<button onclick={() => (state.y = true)}>add y</button>
+<button onclick={() => delete state.y}>delete y</button>
+<p>{Object.hasOwn(state, 'y')}</p>