diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 80c4155705..90f922df68 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -5,6 +5,7 @@ import type {
 	TemplateNode,
 	TransitionManager
 } from '#client';
+import type { Boundary } from '../dom/blocks/boundary';
 
 export interface Signal {
 	/** Flags bitmask */
@@ -84,6 +85,8 @@ export interface Effect extends Reaction {
 	last: null | Effect;
 	/** Parent effect */
 	parent: Effect | null;
+	/** The boundary this effect belongs to */
+	b: Boundary | null;
 	/** Dev only */
 	component_function?: any;
 	/** Dev only. Only set for certain block effects. Contains a reference to the stack that represents the render tree */