diff --git a/bin/generate-tests.php b/bin/generate-tests.php
index b17f47a6..41dea9f4 100755
--- a/bin/generate-tests.php
+++ b/bin/generate-tests.php
@@ -164,6 +164,7 @@
 add_test(['list'], 'LayoutWithOldFolder', '{{ base }}/tests/fixtures/valid/layout-with-old-folder');
 add_test([], 'ImportSamePackageWithDefaultVersion', '{{ base }}/tests/fixtures/valid/import-same-package-with-default-version', needRemote: true, needResetVendor: true);
 add_test(['fs-watch'], 'WatchWithForcedTimeout', '{{ base }}/tests/fixtures/valid/watch-with-forced-timeout');
+add_test([], 'DefaultTask', '{{ base }}/tests/fixtures/valid/default-task');
 
 echo "\nDone.\n";
 
diff --git a/doc/getting-started/basic-usage.md b/doc/getting-started/basic-usage.md
index b3f39ba5..f3a6ea1f 100644
--- a/doc/getting-started/basic-usage.md
+++ b/doc/getting-started/basic-usage.md
@@ -106,7 +106,7 @@ function a_very_long_function_name_that_is_very_painful_to_write(): void
 
 ## Setting a default task
 
-The `Castor\Attribute\AsTask` attribute allows you to set a default task when 
+The `Castor\Attribute\AsTask` attribute allows you to set a default task when
 calling `castor` without any arguments:
 
 ```php
@@ -114,9 +114,13 @@ use Castor\Attribute\AsTask;
 
 use function Castor\io;
 
-#[AsTask(name: 'bar', namespace: 'foo', default: true)]
-function a_very_long_function_name_that_is_very_painful_to_write(): void
+#[AsTask(description: 'Displays some help and available urls for the current project', default: true)]
+function about(): void
 {
-    io()->writeln('Foo bar');
+    io()->title('About this project');
+
+    io()->comment('Run <comment>castor</comment> to display all available commands.');
+    io()->comment('Run <comment>castor about</comment> to display this project help.');
+    io()->comment('Run <comment>castor help [command]</comment> to display Castor help.');
 }
 ```
diff --git a/src/Function/FunctionLoader.php b/src/Function/FunctionLoader.php
index 833bea00..26a9adad 100644
--- a/src/Function/FunctionLoader.php
+++ b/src/Function/FunctionLoader.php
@@ -10,8 +10,8 @@
 use Castor\Descriptor\ListenerDescriptor;
 use Castor\Descriptor\SymfonyTaskDescriptor;
 use Castor\Descriptor\TaskDescriptor;
+use Castor\Exception\FunctionConfigurationException;
 use Castor\Factory\TaskCommandFactory;
-use Psr\Log\LoggerInterface;
 use Symfony\Component\DependencyInjection\Attribute\Autowire;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 
@@ -24,7 +24,6 @@ public function __construct(
         #[Autowire(lazy: true)]
         private readonly Application $application,
         private readonly TaskCommandFactory $taskCommandFactory,
-        private readonly LoggerInterface $logger,
     ) {
     }
 
@@ -78,14 +77,8 @@ public function loadTasks(
                     $taskName = $descriptor->taskAttribute->namespace . ':' . $taskName;
                 }
 
-                if (null !== $previousDefault) {
-                    $this->logger->warning(
-                        \sprintf(
-                            'Task "%s" is marked as default, but task "%s" is already marked as default',
-                            $taskName,
-                            $previousDefault
-                        )
-                    );
+                if ($previousDefault) {
+                    throw new FunctionConfigurationException(\sprintf('The task is marked as default, but task "%s()" was already marked as default.', $previousDefault), $descriptor->function);
                 }
 
                 $previousDefault = $taskName;
diff --git a/tests/Generated/DefaultTaskConflictTest.php b/tests/Generated/DefaultTaskConflictTest.php
new file mode 100644
index 00000000..a5a8e2db
--- /dev/null
+++ b/tests/Generated/DefaultTaskConflictTest.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Castor\Tests\Generated;
+
+use Castor\Tests\TaskTestCase;
+use Symfony\Component\Process\Exception\ProcessFailedException;
+
+class DefaultTaskConflictTest extends TaskTestCase
+{
+    // no task
+    public function test(): void
+    {
+        $process = $this->runTask([], '{{ base }}/tests/fixtures/broken/default-task-conflict', needRemote: true);
+
+        if (1 !== $process->getExitCode()) {
+            throw new ProcessFailedException($process);
+        }
+
+        $this->assertStringEqualsFile(__FILE__ . '.output.txt', $process->getOutput());
+        $this->assertStringEqualsFile(__FILE__ . '.err.txt', $process->getErrorOutput());
+    }
+}
diff --git a/tests/Generated/DefaultTaskConflictTest.php.err.txt b/tests/Generated/DefaultTaskConflictTest.php.err.txt
new file mode 100644
index 00000000..0e561c5e
--- /dev/null
+++ b/tests/Generated/DefaultTaskConflictTest.php.err.txt
@@ -0,0 +1,7 @@
+In FunctionLoader.php line XXXX:
+
+  Function "about2()" is not properly configured:
+  The task is marked as default, but task "about()" was already marked as default.
+  Defined in "castor.php" line 11.
+
+
diff --git a/tests/Generated/DefaultTaskConflictTest.php.output.txt b/tests/Generated/DefaultTaskConflictTest.php.output.txt
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/Generated/DefaultTaskTest.php b/tests/Generated/DefaultTaskTest.php
new file mode 100644
index 00000000..cc670735
--- /dev/null
+++ b/tests/Generated/DefaultTaskTest.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Castor\Tests\Generated;
+
+use Castor\Tests\TaskTestCase;
+use Symfony\Component\Process\Exception\ProcessFailedException;
+
+class DefaultTaskTest extends TaskTestCase
+{
+    // no task
+    public function test(): void
+    {
+        $process = $this->runTask([], '{{ base }}/tests/fixtures/valid/default-task');
+
+        if (0 !== $process->getExitCode()) {
+            throw new ProcessFailedException($process);
+        }
+
+        $this->assertStringEqualsFile(__FILE__ . '.output.txt', $process->getOutput());
+        $this->assertSame('', $process->getErrorOutput());
+    }
+}
diff --git a/tests/Generated/DefaultTaskTest.php.output.txt b/tests/Generated/DefaultTaskTest.php.output.txt
new file mode 100644
index 00000000..09e16f36
--- /dev/null
+++ b/tests/Generated/DefaultTaskTest.php.output.txt
@@ -0,0 +1 @@
+about
diff --git a/tests/fixtures/broken/default-task-conflict/castor.php b/tests/fixtures/broken/default-task-conflict/castor.php
new file mode 100644
index 00000000..82673994
--- /dev/null
+++ b/tests/fixtures/broken/default-task-conflict/castor.php
@@ -0,0 +1,13 @@
+<?php
+
+use Castor\Attribute\AsTask;
+
+#[AsTask(default: true)]
+function about(): void
+{
+}
+
+#[AsTask(default: true)]
+function about2(): void
+{
+}
diff --git a/tests/fixtures/valid/default-task/castor.php b/tests/fixtures/valid/default-task/castor.php
new file mode 100644
index 00000000..10e51527
--- /dev/null
+++ b/tests/fixtures/valid/default-task/castor.php
@@ -0,0 +1,11 @@
+<?php
+
+use Castor\Attribute\AsTask;
+
+use function Castor\io;
+
+#[AsTask(default: true)]
+function about(): void
+{
+    io()->writeln('about');
+}