diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 6525b3e5fb..2c7136ef10 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -47,6 +47,7 @@ import { loop } from '../../loop.js';
 
 export class Boundary {
 	suspended = false;
+	inert = false;
 
 	/** @type {Boundary | null} */
 	parent;
@@ -106,13 +107,7 @@ export class Boundary {
 		this.parent = /** @type {Effect} */ (active_effect).b;
 
 		this.#effect = block(() => {
-			var boundary_effect = /** @type {Effect} */ (active_effect);
-			boundary_effect.b = this;
-
-			// @ts-ignore We re-use the effect's fn property to avoid allocation of an additional field
-			boundary_effect.fn = (/** @type {unknown} */ input) => {
-				this.error(input);
-			};
+			/** @type {Effect} */ (active_effect).b = this;
 
 			if (hydrating) {
 				hydrate_next();
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index acd863c566..d872503ab6 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -252,22 +252,19 @@ export function check_dirtiness(reaction) {
  * @param {Effect} effect
  */
 function propagate_error(error, effect) {
-	/** @type {Effect | null} */
-	var current = effect;
+	var boundary = effect.b;
 
-	while (current !== null) {
-		if ((current.f & BOUNDARY_EFFECT) !== 0) {
+	while (boundary !== null) {
+		if (!boundary.inert) {
 			try {
-				// @ts-expect-error
-				current.fn(error);
+				boundary.error(error);
 				return;
 			} catch {
-				// Remove boundary flag from effect
-				current.f ^= BOUNDARY_EFFECT;
+				boundary.inert = true;
 			}
 		}
 
-		current = current.parent;
+		boundary = boundary.parent;
 	}
 
 	is_throwing_error = false;
@@ -278,10 +275,7 @@ function propagate_error(error, effect) {
  * @param {Effect} effect
  */
 function should_rethrow_error(effect) {
-	return (
-		(effect.f & DESTROYED) === 0 &&
-		(effect.parent === null || (effect.parent.f & BOUNDARY_EFFECT) === 0)
-	);
+	return (effect.f & DESTROYED) === 0 && (effect.parent === null || !effect.b || effect.b.inert);
 }
 
 export function reset_is_throwing_error() {