diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index e3f4bd161a..fa2903414f 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -242,9 +242,6 @@ export class Boundary {
 
 		this.ran = true;
 
-		// @ts-expect-error
-		this.#effect.fn.boundary = this;
-
 		if (hydrating) {
 			this.#anchor = hydrate_node;
 		}
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 4027a094ad..acd863c566 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -829,8 +829,7 @@ function process_effects(effect, collected_effects, boundary) {
 				// Inside a boundary, defer everything except block/branch effects
 				boundary.add_effect(current_effect);
 			} else if ((flags & BOUNDARY_EFFECT) !== 0) {
-				// @ts-expect-error
-				var b = /** @type {Boundary} */ (current_effect.fn.boundary);
+				var b = /** @type {Boundary} */ (current_effect.b);
 
 				process_effects(current_effect, collected_effects, b);