diff --git a/src/EditRegistration/Type.php b/src/EditRegistration/Type.php
index ef36e6f..c7940f8 100644
--- a/src/EditRegistration/Type.php
+++ b/src/EditRegistration/Type.php
@@ -12,6 +12,7 @@ class Type extends AbstractType
     use TypeHasCategoriesElementTrait;
 
     public const ELEMENT_CATEGORIES = 'categories';
+    protected CategoryRepositoryInterface $categoryRepository;
 
     public function __construct(CategoryRepositoryInterface $categoryRepository)
     {
@@ -20,7 +21,11 @@ public function __construct(CategoryRepositoryInterface $categoryRepository)
 
     public function buildForm(FormBuilderInterface $builder, array $options): void
     {
-        $this->addCategoriesElementToForm($builder, false);
+        $choices = $this->categoryRepository->findVisible();
+
+        if (\count($choices) > 1) {
+            $this->addCategoriesElementToForm($builder, $choices, false);
+        }
 
         // We need at least one element in addition to the categories above, so that Symfony recognizes the form being
         // submitted even if no categories where chosen.
diff --git a/src/EditRegistration/TypeHasCategoriesElementTrait.php b/src/EditRegistration/TypeHasCategoriesElementTrait.php
index cc061aa..4f7a204 100644
--- a/src/EditRegistration/TypeHasCategoriesElementTrait.php
+++ b/src/EditRegistration/TypeHasCategoriesElementTrait.php
@@ -5,20 +5,11 @@
 use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
 use Symfony\Component\Form\FormBuilderInterface;
 use Symfony\Component\Validator\Constraints\Choice;
-use Webfactory\NewsletterRegistrationBundle\Entity\CategoryRepositoryInterface;
 
 trait TypeHasCategoriesElementTrait
 {
-    protected CategoryRepositoryInterface $categoryRepository;
-
-    protected function addCategoriesElementToForm(FormBuilderInterface $builder, bool $recipientHasToChooseAtLeastOne)
+    protected function addCategoriesElementToForm(FormBuilderInterface $builder, array $choices, bool $recipientHasToChooseAtLeastOne): void
     {
-        // add category choices, if there is more than one
-        $choices = $this->categoryRepository->findVisible();
-        if (\count($choices) < 2) {
-            return;
-        }
-
         $constraints = [];
         if (true === $recipientHasToChooseAtLeastOne) {
             $constraints[] = new Choice(choices: $choices, multiple: true, min: 1);
diff --git a/src/StartRegistration/Type.php b/src/StartRegistration/Type.php
index 4efaa33..74a40d3 100644
--- a/src/StartRegistration/Type.php
+++ b/src/StartRegistration/Type.php
@@ -19,6 +19,7 @@ class Type extends AbstractType
     public const ELEMENT_HONEYPOT = 'url';
 
     protected PendingOptInFactoryInterface $pendingOptInFactory;
+    protected CategoryRepositoryInterface $categoryRepository;
 
     public function __construct(CategoryRepositoryInterface $categoryRepository, PendingOptInFactoryInterface $pendingOptInFactory)
     {
@@ -30,7 +31,11 @@ public function buildForm(FormBuilderInterface $builder, array $options): void
     {
         $builder->add(static::ELEMENT_EMAIL_ADDRESS, EmailAddressType::class);
 
-        $this->addCategoriesElementToForm($builder, true);
+        $choices = $this->categoryRepository->findVisible();
+
+        if (\count($choices) > 1) {
+            $this->addCategoriesElementToForm($builder, $choices, true);
+        }
 
         // fake field for spam protection
         $builder->add(static::ELEMENT_HONEYPOT, HoneypotType::class);
@@ -47,7 +52,14 @@ function (?PendingOptInInterface $pendingOptIn): array {
                     static::ELEMENT_CATEGORIES => $pendingOptIn->getCategories(),
                 ];
             },
-            function (array $formData) use ($that): ?PendingOptInInterface {
+            function (array $formData) use ($that, $choices): ?PendingOptInInterface {
+                if (!isset($formData[self::ELEMENT_CATEGORIES]) && 1 === \count($choices)) {
+                    // if the field 'categories' is not in the form because you could choose only one anyway, we need to
+                    // set that one category here.
+                    $singleCategory = $choices[0];
+                    $formData[self::ELEMENT_CATEGORIES] = [$singleCategory];
+                }
+
                 return $that->pendingOptInFactory->fromRegistrationFormData($formData);
             }
         ));
diff --git a/tests/StartRegistration/TypeTest.php b/tests/StartRegistration/TypeTest.php
index 02dad28..9bc6d2b 100644
--- a/tests/StartRegistration/TypeTest.php
+++ b/tests/StartRegistration/TypeTest.php
@@ -240,6 +240,34 @@ function (array $formData) {
         $this->assertEquals($pendingOptIn, $form->getData());
     }
 
+    #[Test]
+    public function provides_PendingOptIn_with_single_category_auto_assigned_when_only_one_exists(): void
+    {
+        $this->setUpOneCategory();
+
+        $pendingOptIn = new PendingOptIn(null, new EmailAddress('webfactory@example.com', 'secret'), [$this->category1]);
+        $this->pendingOptInFactory
+            ->method('fromRegistrationFormData')
+            ->with(
+                $this->callback(
+                    function (array $formData) {
+                        return \array_key_exists(StartRegistrationType::ELEMENT_CATEGORIES, $formData)
+                            && $formData[StartRegistrationType::ELEMENT_CATEGORIES] === [$this->category1];
+                    }
+                )
+            )
+            ->willReturn($pendingOptIn);
+
+        $form = $this->factory->create(StartRegistrationType::class);
+        $form->submit([
+            StartRegistrationType::ELEMENT_EMAIL_ADDRESS => 'webfactory@example.com',
+            StartRegistrationType::ELEMENT_HONEYPOT => '',
+        ]);
+
+        $this->assertTrue($form->isValid());
+        $this->assertEquals($pendingOptIn, $form->getData());
+    }
+
     #[Test]
     public function provides_PendingOptIn_if_submitted_with_valid_data_and_category_choices()
     {