diff --git a/src/manager/event_manager.ts b/src/manager/event_manager.ts
index a772683..e937e89 100644
--- a/src/manager/event_manager.ts
+++ b/src/manager/event_manager.ts
@@ -11,6 +11,7 @@ import {logDebug} from '../utils/log.js';
 import {prefs} from '../utils/settings.js';
 import {hasMetaWindow, type RoundedWindowActor} from '../utils/types.js';
 import * as handlers from './event_handlers.js';
+import {unwrapActor} from './utils.js';
 
 /**
  * The rounded corners effect has to perform some actions when differen events
@@ -141,11 +142,15 @@ function disconnectAll(object?: GObject.Object | null) {
 function applyEffectTo(actor: RoundedWindowActor) {
     // In wayland sessions, the surface actor of XWayland clients is sometimes
     // not ready when the window is created. In this case, we wait until it is
-    // ready before applying the effect.
-    if (!actor.firstChild) {
-        const id = actor.connect('notify::first-child', () => {
-            applyEffectTo(actor);
+    // ready before applying the effect. `child-added` is used instead of
+    // `notify::first-child` because another extension may already occupy the
+    // first child slot.
+    if (!unwrapActor(actor)) {
+        const id = actor.connect('child-added', () => {
+            if (!unwrapActor(actor)) return;
+
             actor.disconnect(id);
+            applyEffectTo(actor);
         });
 
         return;
diff --git a/src/manager/utils.ts b/src/manager/utils.ts
index 37d822f..8e5ff49 100644
--- a/src/manager/utils.ts
+++ b/src/manager/utils.ts
@@ -1,6 +1,5 @@
 /** @file Provides various utility functions used withing signal handling code. */
 
-import type St from 'gi://St';
 import type {RoundedCornersEffect} from '../effect/rounded_corners_effect.js';
 import type {
     BoxShadow,
@@ -10,6 +9,7 @@ import type {
 
 import Gio from 'gi://Gio';
 import Meta from 'gi://Meta';
+import St from 'gi://St';
 
 import {boxShadowCss} from '../utils/box_shadow.js';
 import {
@@ -22,16 +22,20 @@ import {logDebug} from '../utils/log.js';
 import {getPref} from '../utils/settings.js';
 
 /**
- * Get the actor that rounded corners should be applied to.
- * In Wayland, the effect is applied to WindowActor, but in X11, it is applied
- * to WindowActor.first_child.
+ * Get the actor that rounded corners should be applied to: the MetaSurfaceActor
+ * holding the window contents, rather than the window actor itself. The effect
+ * is an offscreen effect, so attaching it to the window actor would also
+ * capture actors that other extensions insert into it, such as Blur my Shell's
+ * blur actor, which then has nothing left to blur. MetaSurfaceActor isn't
+ * introspectable, so it is matched by skipping those injected actors, which are
+ * always StWidgets.
  *
  * @param actor - The window actor to unwrap.
- * @returns The correct actor that the effect should be applied to.
+ * @returns The actor to apply the effect to, or `undefined` if the window
+ * contents don't exist yet.
  */
 export function unwrapActor(actor: RoundedWindowActor) {
-    const type = actor.metaWindow.get_client_type();
-    return type === Meta.WindowClientType.X11 ? actor.get_first_child() : actor;
+    return actor.get_children().find(child => !(child instanceof St.Widget));
 }
 
 /**
@@ -67,14 +71,9 @@ type RoundedCornersEffectType = InstanceType<typeof RoundedCornersEffect>;
  * @returns The corresponding Clutter.Effect object.
  */
 export function getRoundedCornersEffect(actor: RoundedWindowActor) {
-    const win = actor.metaWindow;
-    const name = ROUNDED_CORNERS_EFFECT;
-    const isXwayland =
-        win.get_client_type() === Meta.WindowClientType.X11 && actor.firstChild;
-
-    return isXwayland
-        ? (actor.firstChild.get_effect(name) as RoundedCornersEffectType)
-        : (actor.get_effect(name) as RoundedCornersEffectType);
+    return unwrapActor(actor)?.get_effect(
+        ROUNDED_CORNERS_EFFECT,
+    ) as RoundedCornersEffectType | null;
 }
 
 /** Compute outer bounds for rounded corners of a window