diff --git a/.changeset/sixty-pandas-rush.md b/.changeset/sixty-pandas-rush.md
new file mode 100644
index 0000000000..0bae18c06c
--- /dev/null
+++ b/.changeset/sixty-pandas-rush.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: optimize object property mutations in compilation
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/global.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/global.js
index c299dd99ef..811407b35b 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/global.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/global.js
@@ -105,6 +105,8 @@ export const global_visitors = {
 			if (serialized_assignment === assignment) {
 				// No change to output -> nothing to transform -> we can keep the original update expression
 				return next();
+			} else if (context.state.analysis.runes) {
+				return serialized_assignment;
 			} else {
 				/** @type {import('estree').Statement[]} */
 				let statements;