diff --git a/.changeset/evil-stars-wave.md b/.changeset/evil-stars-wave.md
new file mode 100644
index 0000000000..b199afe1dd
--- /dev/null
+++ b/.changeset/evil-stars-wave.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: transfer effects when merging batches
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index ae4f5a6dac..2803ffc84c 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -289,19 +289,19 @@ export class Batch {
 			}
 		}
 
-		// we only reschedule previously-deferred effects if we expect
-		// to be able to run them after processing the batch
-		if (!this.#is_deferred()) {
-			for (const e of this.#dirty_effects) {
-				this.#maybe_dirty_effects.delete(e);
-				set_signal_status(e, DIRTY);
-				this.schedule(e);
-			}
+		// We always reschedule previously-deferred effects, not just when
+		// #is_deferred() is true, because traversing the tree could make
+		// an if block that contains the last blocking pending effect falsy,
+		// causing the block to no longer be deferred.
+		for (const e of this.#dirty_effects) {
+			this.#maybe_dirty_effects.delete(e);
+			set_signal_status(e, DIRTY);
+			this.schedule(e);
+		}
 
-			for (const e of this.#maybe_dirty_effects) {
-				set_signal_status(e, MAYBE_DIRTY);
-				this.schedule(e);
-			}
+		for (const e of this.#maybe_dirty_effects) {
+			set_signal_status(e, MAYBE_DIRTY);
+			this.schedule(e);
 		}
 
 		const roots = this.#roots;
@@ -362,6 +362,10 @@ export class Batch {
 		const earlier_batch = this.#find_earlier_batch();
 
 		if (earlier_batch) {
+			// If this batch collected deferred effects during traversal, they still need
+			// to run after being merged into the earlier batch.
+			this.#defer_effects(render_effects);
+			this.#defer_effects(effects);
 			earlier_batch.#merge(this);
 			return;
 		}
@@ -503,6 +507,9 @@ export class Batch {
 			if (d) deferred.promise.then(d.resolve);
 		}
 
+		// Mark is not guaranteed not touch these, so we transfer them
+		this.transfer_effects(batch.#dirty_effects, batch.#maybe_dirty_effects);
+
 		/**
 		 * mark all effects that depend on `batch.current`, except the
 		 * async effects that we just resolved (TODO unless they depend
diff --git a/packages/svelte/tests/runtime-runes/samples/async-batch-merge-effect/_config.js b/packages/svelte/tests/runtime-runes/samples/async-batch-merge-effect/_config.js
new file mode 100644
index 0000000000..c2be623de2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-batch-merge-effect/_config.js
@@ -0,0 +1,25 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		const [x, x_y, pop] = target.querySelectorAll('button');
+
+		x.click();
+		await tick();
+		x_y.click();
+		await tick();
+		pop.click();
+		await tick();
+		pop.click();
+		await tick();
+		pop.click();
+		await tick();
+
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>x</button> <button>x/y</button> <button>pop</button> 2 1 1'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-batch-merge-effect/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-batch-merge-effect/main.svelte
new file mode 100644
index 0000000000..61efd4fca0
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-batch-merge-effect/main.svelte
@@ -0,0 +1,25 @@
+<script>
+	let x = $state(0);
+	let y = $state(0);
+
+	const queued = [];
+
+	function push(v) {
+		if (v === 0) return v;
+
+		return new Promise((fulfil) => {
+			queued.push(() => fulfil(v));
+		});
+	}
+</script>
+
+<button onclick={() => x++}>x</button>
+<button onclick={() => {x++;y++}}>x/y</button>
+<button onclick={() => (queued.pop()?.())}>pop</button>
+
+{await push(x)} {await push(y)}
+
+{#if true}
+	{y}
+{/if}
+