diff --git a/packages/svelte/src/compiler/phases/3-transform/client/utils.js b/packages/svelte/src/compiler/phases/3-transform/client/utils.js
index 7d662629da..d1a825d231 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/utils.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/utils.js
@@ -47,19 +47,10 @@ export function build_getter(node, state) {
 
 /**
  * @param {Expression} value
- * @param {PrivateIdentifier | string} proxy_reference
+ * @param {Expression} previous
  */
-export function build_proxy_reassignment(value, proxy_reference) {
-	return dev
-		? b.call(
-				'$.proxy',
-				value,
-				b.null,
-				typeof proxy_reference === 'string'
-					? b.id(proxy_reference)
-					: b.member(b.this, proxy_reference)
-			)
-		: b.call('$.proxy', value);
+export function build_proxy_reassignment(value, previous) {
+	return dev ? b.call('$.proxy', value, b.null, previous) : b.call('$.proxy', value);
 }
 
 /**
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js
index e4c630adb6..cf54dba1b3 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js
@@ -48,7 +48,7 @@ function build_assignment(operator, left, right, context) {
 					value =
 						private_state.kind === 'raw_state'
 							? value
-							: build_proxy_reassignment(value, private_state.id);
+							: build_proxy_reassignment(value, b.member(b.this, private_state.id));
 				}
 
 				if (!context.state.in_constructor) {
@@ -95,7 +95,7 @@ function build_assignment(operator, left, right, context) {
 			context.state.analysis.runes &&
 			should_proxy(value, context.state.scope)
 		) {
-			value = binding.kind === 'raw_state' ? value : build_proxy_reassignment(value, object.name);
+			value = binding.kind === 'raw_state' ? value : build_proxy_reassignment(value, object);
 		}
 
 		return transform.assign(object, value);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/ClassBody.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/ClassBody.js
index 5342e70aac..49df730ee6 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/ClassBody.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/ClassBody.js
@@ -139,12 +139,14 @@ export function ClassBody(node, context) {
 					if (field.kind === 'state') {
 						// set foo(value) { this.#foo = value; }
 						const value = b.id('value');
+						const prev = b.member(b.this, field.id);
+
 						body.push(
 							b.method(
 								'set',
 								definition.key,
 								[value],
-								[b.stmt(b.call('$.set', member, build_proxy_reassignment(value, field.id)))]
+								[b.stmt(b.call('$.set', member, build_proxy_reassignment(value, prev)))]
 							)
 						);
 					}