diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 806f9a324a..c09784d2c2 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -90,7 +90,7 @@ export function proxy(value, onchange) {
 	if (is_proxied_array) {
 		// We need to create the length source eagerly to ensure that
 		// mutations to the array are properly synced with our proxy
-		sources.set('length', source(/** @type {any[]} */ (value).length, onchange, stack));
+		sources.set('length', source(/** @type {any[]} */ (value).length, stack));
 	}
 
 	return new Proxy(/** @type {any} */ (value), {
@@ -111,7 +111,7 @@ export function proxy(value, onchange) {
 			var s = sources.get(prop);
 
 			if (s === undefined) {
-				s = with_parent(() => source(descriptor.value, onchange, stack));
+				s = with_parent(() => source(descriptor.value, stack));
 				sources.set(prop, s);
 			} else {
 				set(
@@ -130,7 +130,7 @@ export function proxy(value, onchange) {
 				if (prop in target) {
 					sources.set(
 						prop,
-						with_parent(() => source(UNINITIALIZED, onchange, stack))
+						with_parent(() => source(UNINITIALIZED, stack))
 					);
 				}
 			} else {
@@ -182,9 +182,8 @@ export function proxy(value, onchange) {
 
 			// create a source, but only if it's an own property and not a prototype property
 			if (s === undefined && (!exists || get_descriptor(target, prop)?.writable)) {
-				let opt = onchange;
 				s = with_parent(() =>
-					source(proxy(exists ? target[prop] : UNINITIALIZED, opt), opt, stack)
+					source(proxy(exists ? target[prop] : UNINITIALIZED, onchange), stack)
 				);
 				sources.set(prop, s);
 			}
@@ -243,8 +242,7 @@ export function proxy(value, onchange) {
 				(active_effect !== null && (!has || get_descriptor(target, prop)?.writable))
 			) {
 				if (s === undefined) {
-					let opt = onchange;
-					s = with_parent(() => source(has ? proxy(target[prop], opt) : UNINITIALIZED, opt, stack));
+					s = with_parent(() => source(has ? proxy(target[prop], onchange) : UNINITIALIZED, stack));
 					sources.set(prop, s);
 				}
 
@@ -283,7 +281,7 @@ export function proxy(value, onchange) {
 							// If the item exists in the original, we need to create a uninitialized source,
 							// else a later read of the property would result in a source being created with
 							// the value of the original item at that index.
-							other_s = with_parent(() => source(UNINITIALIZED, onchange, stack));
+							other_s = with_parent(() => source(UNINITIALIZED, stack));
 							sources.set(i + '', other_s);
 						}
 					}
@@ -295,7 +293,7 @@ export function proxy(value, onchange) {
 				// object property before writing to that property.
 				if (s === undefined) {
 					if (!has || get_descriptor(target, prop)?.writable) {
-						s = with_parent(() => source(undefined, onchange, stack));
+						s = with_parent(() => source(undefined, stack));
 						sources.set(prop, s);
 					}
 				} else {
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index ef6d0405ec..6fc459c843 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -76,12 +76,11 @@ export function batch_onchange(fn) {
 /**
  * @template V
  * @param {V} v
- * @param {() => void} [o]
  * @param {Error | null} [stack]
  * @returns {Source<V>}
  */
 // TODO rename this to `state` throughout the codebase
-export function source(v, o, stack) {
+export function source(v, stack) {
 	/** @type {Value} */
 	var signal = {
 		f: 0, // TODO ideally we could skip this altogether, but it causes type errors
@@ -89,8 +88,7 @@ export function source(v, o, stack) {
 		reactions: null,
 		equals,
 		rv: 0,
-		wv: 0,
-		o
+		wv: 0
 	};
 
 	if (DEV && tracing_mode_flag) {
@@ -109,7 +107,8 @@ export function source(v, o, stack) {
  */
 /*#__NO_SIDE_EFFECTS__*/
 export function state(v, o, stack) {
-	const s = source(v, o, stack);
+	const s = source(v, stack);
+	if (o) s.o = o;
 
 	push_reaction_value(s);