diff --git a/src/Symfony/Bundle/DependencyInjection/Configuration.php b/src/Symfony/Bundle/DependencyInjection/Configuration.php
index cc7326d2e6..44f08739e5 100644
--- a/src/Symfony/Bundle/DependencyInjection/Configuration.php
+++ b/src/Symfony/Bundle/DependencyInjection/Configuration.php
@@ -663,6 +663,17 @@ private function addDefaultsSection(ArrayNodeDefinition $rootNode): void
                 }
 
                 return $normalizedDefaults;
+            })
+            ->end()
+            ->validate()
+            ->always(static function (array $defaults): array {
+                foreach (['mcp', 'graph_ql_operations', 'state_options', 'links', 'openapi'] as $option) {
+                    if (null !== ($defaults[$option] ?? null) && ('openapi' !== $option || !\is_bool($defaults[$option]))) {
+                        throw new InvalidConfigurationException(\sprintf('The "defaults.%s" option is not supported, it needs objects. Set it on the resources instead.', $option));
+                    }
+                }
+
+                return $defaults;
             });
 
         $this->defineDefault($defaultsNode, new \ReflectionClass(ApiResource::class), $nameConverter);
diff --git a/tests/Symfony/Bundle/DependencyInjection/ConfigurationTest.php b/tests/Symfony/Bundle/DependencyInjection/ConfigurationTest.php
index 24c952b015..ee90abfd62 100644
--- a/tests/Symfony/Bundle/DependencyInjection/ConfigurationTest.php
+++ b/tests/Symfony/Bundle/DependencyInjection/ConfigurationTest.php
@@ -277,6 +277,39 @@ public function testExceptionToStatusConfigWithInvalidHttpStatusCode($invalidHtt
         ]);
     }
 
+    public static function objectDefaultProvider(): iterable
+    {
+        yield 'mcp' => ['mcp', ['tool' => ['description' => 'Get a book']]];
+        yield 'graph_ql_operations' => ['graph_ql_operations', [['class' => 'ApiPlatform\Metadata\GraphQl\Query']]];
+        yield 'state_options' => ['state_options', ['entity_class' => 'App\Entity\Book']];
+        yield 'links' => ['links', [['rel' => 'preload', 'href' => '/books']]];
+        yield 'openapi' => ['openapi', ['summary' => 'A book']];
+    }
+
+    #[DataProvider('objectDefaultProvider')]
+    public function testDefaultsThatNeedObjects(string $key, array $value): void
+    {
+        $this->expectException(InvalidConfigurationException::class);
+        $this->expectExceptionMessage(\sprintf('The "defaults.%s" option is not supported, it needs objects. Set it on the resources instead.', $key));
+
+        $this->processor->processConfiguration($this->configuration, [
+            'api_platform' => [
+                'defaults' => [$key => $value],
+            ],
+        ]);
+    }
+
+    public function testOpenapiDefaultCanBeABoolean(): void
+    {
+        $config = $this->processor->processConfiguration($this->configuration, [
+            'api_platform' => [
+                'defaults' => ['openapi' => false],
+            ],
+        ]);
+
+        $this->assertFalse($config['defaults']['openapi']);
+    }
+
     public static function invalidHttpStatusCodeValueProvider(): array
     {
         return [