diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 48d5855470..a194b093e7 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -44,7 +44,7 @@ export let active_boundary = null;
 export function set_active_boundary(boundary) {
 	active_boundary = boundary;
 }
-class Boundary {
+export class Boundary {
 	/** @type {Boundary | null} */
 	#parent;
 
@@ -54,6 +54,12 @@ class Boundary {
 	/** @type {Set<() => void>} */
 	#callbacks = new Set();
 
+	/** @type {Effect[]} */
+	#render_effects = [];
+
+	/** @type {Effect[]} */
+	#effects = [];
+
 	/**
 	 * @param {TemplateNode} node
 	 * @param {{
@@ -90,12 +96,6 @@ class Boundary {
 			var hydrate_open = hydrate_node;
 			var is_creating_fallback = false;
 
-			/** @type {Effect[]} */
-			var render_effects = [];
-
-			/** @type {Effect[]} */
-			var effects = [];
-
 			var keep_pending_snippet = false;
 
 			/**
@@ -156,7 +156,7 @@ class Boundary {
 					boundary_effect.f ^= BOUNDARY_SUSPENDED;
 				}
 
-				for (const e of render_effects) {
+				for (const e of this.#render_effects) {
 					try {
 						if (check_dirtiness(e)) {
 							update_effect(e);
@@ -180,7 +180,7 @@ class Boundary {
 					offscreen_fragment = null;
 				}
 
-				for (const e of effects) {
+				for (const e of this.#effects) {
 					try {
 						if (check_dirtiness(e)) {
 							update_effect(e);
@@ -270,12 +270,12 @@ class Boundary {
 				}
 
 				if (input === ADD_RENDER_EFFECT) {
-					render_effects.push(payload);
+					this.#render_effects.push(payload);
 					return;
 				}
 
 				if (input === ADD_EFFECT) {
-					effects.push(payload);
+					this.#effects.push(payload);
 					return;
 				}
 
@@ -370,6 +370,9 @@ class Boundary {
 			reset_is_throwing_error();
 		}, flags);
 
+		// @ts-expect-error
+		this.#effect.fn.boundary = this;
+
 		if (hydrating) {
 			anchor = hydrate_node;
 		}
@@ -405,6 +408,11 @@ class Boundary {
 	add_callback(fn) {
 		this.#callbacks.add(fn);
 	}
+
+	/** @param {Effect} effect */
+	add_effect(effect) {
+		((effect.f & RENDER_EFFECT) !== 0 ? this.#render_effects : this.#effects).push(effect);
+	}
 }
 
 const ASYNC_INCREMENT = Symbol();
@@ -526,15 +534,6 @@ function exit() {
 	set_component_context(null);
 }
 
-/**
- * @param {Effect} boundary
- * @param {Effect} effect
- */
-export function add_boundary_effect(boundary, effect) {
-	// @ts-ignore
-	boundary.fn((effect.f & RENDER_EFFECT) !== 0 ? ADD_RENDER_EFFECT : ADD_EFFECT, effect);
-}
-
 /**
  * @param {Effect} boundary
  */
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 8016eeb9b2..706b8da25b 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -50,7 +50,7 @@ import {
 	set_component_context,
 	set_dev_current_component_function
 } from './context.js';
-import { add_boundary_effect, commit_boundary } from './dom/blocks/boundary.js';
+import { Boundary, commit_boundary } from './dom/blocks/boundary.js';
 import * as w from './warnings.js';
 
 const FLUSH_MICROTASK = 0;
@@ -812,7 +812,7 @@ export function schedule_effect(signal) {
  *
  * @param {Effect} effect
  * @param {Effect[]} collected_effects
- * @param {Effect} [boundary]
+ * @param {Boundary} [boundary]
  * @returns {void}
  */
 function process_effects(effect, collected_effects, boundary) {
@@ -828,9 +828,10 @@ function process_effects(effect, collected_effects, boundary) {
 		if (!is_skippable_branch && (flags & INERT) === 0) {
 			if (boundary !== undefined && (flags & (BLOCK_EFFECT | BRANCH_EFFECT)) === 0) {
 				// Inside a boundary, defer everything except block/branch effects
-				add_boundary_effect(/** @type {Effect} */ (boundary), current_effect);
+				boundary.add_effect(current_effect);
 			} else if ((flags & BOUNDARY_EFFECT) !== 0) {
-				process_effects(current_effect, collected_effects, current_effect);
+				// @ts-expect-error
+				process_effects(current_effect, collected_effects, current_effect.fn.boundary);
 
 				if ((current_effect.f & BOUNDARY_SUSPENDED) === 0) {
 					// no more async work to happen