diff --git a/.changeset/fix-memory-leak-boundary.md b/.changeset/fix-memory-leak-boundary.md
new file mode 100644
index 0000000000..8a3b084981
--- /dev/null
+++ b/.changeset/fix-memory-leak-boundary.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: null out `effect.b` in `destroy_effect`
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index aeffeedddd..54c8a17d79 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -559,6 +559,7 @@ export function destroy_effect(effect, remove_dom = true) {
 		effect.fn =
 		effect.nodes =
 		effect.ac =
+		effect.b =
 			null;
 }