diff --git a/.changeset/polite-melons-tickle.md b/.changeset/polite-melons-tickle.md
new file mode 100644
index 000000000000..42967ea936d3
--- /dev/null
+++ b/.changeset/polite-melons-tickle.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: avoid microtasks when flushing sync
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 7a926bf62457..87a69cb851e0 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -47,6 +47,7 @@ const handled_errors = new WeakSet();
 let is_throwing_error = false;
 
 let is_flushing = false;
+let is_flushing_sync = false;
 
 /** @type {Effect | null} */
 let last_scheduled_effect = null;
@@ -734,7 +735,9 @@ function flush_queued_effects(effects) {
 export function schedule_effect(signal) {
 	if (!is_flushing) {
 		is_flushing = true;
-		queueMicrotask(flush_queued_root_effects);
+		if (!is_flushing_sync) {
+			queueMicrotask(flush_queued_root_effects);
+		}
 	}
 
 	var effect = (last_scheduled_effect = signal);
@@ -818,23 +821,30 @@ function process_effects(root) {
  * @returns {T}
  */
 export function flushSync(fn) {
-	var result;
+	var previously_flushing_sync = is_flushing_sync;
 
-	if (fn) {
-		is_flushing = true;
-		flush_queued_root_effects();
-		result = fn();
-	}
+	try {
+		var result;
+		is_flushing_sync = true;
 
-	flush_tasks();
+		if (fn) {
+			is_flushing = true;
+			flush_queued_root_effects();
+			result = fn();
+		}
 
-	while (queued_root_effects.length > 0) {
-		is_flushing = true;
-		flush_queued_root_effects();
 		flush_tasks();
-	}
 
-	return /** @type {T} */ (result);
+		while (queued_root_effects.length > 0) {
+			is_flushing = true;
+			flush_queued_root_effects();
+			flush_tasks();
+		}
+
+		return /** @type {T} */ (result);
+	} finally {
+		is_flushing_sync = previously_flushing_sync;
+	}
 }
 
 /**