diff --git a/src/LiveComponent/src/EventListener/DeferLiveComponentSubscriber.php b/src/LiveComponent/src/EventListener/DeferLiveComponentSubscriber.php
index bfc90d68ad9..c585caa6f25 100644
--- a/src/LiveComponent/src/EventListener/DeferLiveComponentSubscriber.php
+++ b/src/LiveComponent/src/EventListener/DeferLiveComponentSubscriber.php
@@ -33,7 +33,7 @@ public function onPostMount(PostMountEvent $event): void
         $data = $event->getData();
 
         if (\array_key_exists('defer', $data)) {
-            trigger_deprecation('symfony/ux-live-component', '2.17', 'The "defer" attribute is deprecated and will be removed in 3.0. Use the "loading" attribute instead set to the value "defer"');
+            trigger_deprecation('symfony/ux-live-component', '2.17', 'The "defer" attribute is deprecated and will be removed in 3.0. Use the "loading" attribute instead set to the value "defer".');
             if ($data['defer']) {
                 $event->addExtraMetadata('loading', 'defer');
             }
@@ -41,8 +41,15 @@ public function onPostMount(PostMountEvent $event): void
         }
 
         if (\array_key_exists('loading', $data)) {
-            if (\in_array($data['loading'], ['defer', 'lazy'], true)) {
-                $event->addExtraMetadata('loading', $data['loading']);
+            // Ignored values: false / null / ''
+            if ($loading = $data['loading']) {
+                if (!\is_scalar($loading)) {
+                    throw new \InvalidArgumentException(sprintf('The "loading" attribute value must be scalar, "%s" passed.', get_debug_type($loading)));
+                }
+                if (!\in_array($loading, ['defer', 'lazy'], true)) {
+                    throw new \InvalidArgumentException(sprintf('Invalid "loading" attribute value "%s". Accepted values: "defer" and "lazy".', $loading));
+                }
+                $event->addExtraMetadata('loading', $loading);
             }
             unset($data['loading']);
         }
diff --git a/src/LiveComponent/tests/Functional/EventListener/DeferLiveComponentSubscriberTest.php b/src/LiveComponent/tests/Functional/EventListener/DeferLiveComponentSubscriberTest.php
index 5175679b4d3..c06b23d9660 100644
--- a/src/LiveComponent/tests/Functional/EventListener/DeferLiveComponentSubscriberTest.php
+++ b/src/LiveComponent/tests/Functional/EventListener/DeferLiveComponentSubscriberTest.php
@@ -141,8 +141,7 @@ public static function provideLoadingValues(): iterable
     {
         return [
             ['lazy', false],
-            ['eager', true],
-            ['foo', true],
+            [false, true],
             ['', true],
         ];
     }
diff --git a/src/LiveComponent/tests/Unit/EventListener/DeferLiveComponentSubscriberTest.php b/src/LiveComponent/tests/Unit/EventListener/DeferLiveComponentSubscriberTest.php
index 218a54c50e7..eb2dd082084 100644
--- a/src/LiveComponent/tests/Unit/EventListener/DeferLiveComponentSubscriberTest.php
+++ b/src/LiveComponent/tests/Unit/EventListener/DeferLiveComponentSubscriberTest.php
@@ -44,7 +44,7 @@ public function testLoadingAttributeOverrideDeferAttribute()
         $subscriber = new DeferLiveComponentSubscriber();
         $event = $this->createPostMountEvent(['loading' => 'lazy', 'defer' => true]);
 
-        $this->expectDeprecation('Since symfony/ux-live-component 2.17: The "defer" attribute is deprecated and will be removed in 3.0. Use the "loading" attribute instead.');
+        $this->expectDeprecation('Since symfony/ux-live-component 2.17: The "defer" attribute is deprecated and will be removed in 3.0. Use the "loading" attribute instead set to the value "defer".');
 
         $subscriber->onPostMount($event);
 
@@ -62,7 +62,7 @@ public function testDeferAttributeTriggerDeprecation()
             'defer' => true,
         ]);
 
-        $this->expectDeprecation('Since symfony/ux-live-component 2.17: The "defer" attribute is deprecated and will be removed in 3.0. Use the "loading" attribute instead.');
+        $this->expectDeprecation('Since symfony/ux-live-component 2.17: The "defer" attribute is deprecated and will be removed in 3.0. Use the "loading" attribute instead set to the value "defer".');
 
         $subscriber->onPostMount($event);
     }
@@ -83,6 +83,31 @@ public function testLoadingAttributesAreRemoved()
         $this->assertArrayNotHasKey('loading-tag', $event->getData());
     }
 
+    /**
+     * @dataProvider provideInvalidLoadingValues
+     */
+    public function testInvalidLoadingValuesThrows(mixed $value)
+    {
+        $subscriber = new DeferLiveComponentSubscriber();
+        $event = $this->createPostMountEvent([
+            'loading' => $value,
+        ]);
+
+        $this->expectException(\InvalidArgumentException::class);
+
+        $subscriber->onPostMount($event);
+    }
+
+    public static function provideInvalidLoadingValues()
+    {
+        return [
+            ['foo'],
+            [true],
+            [['foo']],
+            ['false'],
+        ];
+    }
+
     private function createPostMountEvent(array $data): PostMountEvent
     {
         $componentMetadata = new ComponentMetadata([]);