diff --git a/.changeset/dull-pots-add.md b/.changeset/dull-pots-add.md
new file mode 100644
index 0000000000..c993f2532b
--- /dev/null
+++ b/.changeset/dull-pots-add.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: don't override instance methods during legacy class creation
diff --git a/packages/svelte/src/legacy/legacy-client.js b/packages/svelte/src/legacy/legacy-client.js
index 12c6c61b39..775a9e1517 100644
--- a/packages/svelte/src/legacy/legacy-client.js
+++ b/packages/svelte/src/legacy/legacy-client.js
@@ -79,6 +79,7 @@ class Svelte4Component {
 		});
 
 		for (const key of Object.keys(this.#instance)) {
+			if (key === '$set' || key === '$destroy' || key === '$on') continue;
 			define_property(this, key, {
 				get() {
 					return this.#instance[key];