diff --git a/src/Symfony/Component/Form/ButtonBuilder.php b/src/Symfony/Component/Form/ButtonBuilder.php
index 01f886a0fc299..33bbbdc36de59 100644
--- a/src/Symfony/Component/Form/ButtonBuilder.php
+++ b/src/Symfony/Component/Form/ButtonBuilder.php
@@ -79,9 +79,6 @@ public function __construct(?string $name, array $options = [])
      *
      * This method should not be invoked.
      *
-     * @param string|FormBuilderInterface $child
-     * @param string|FormTypeInterface    $type
-     *
      * @throws BadMethodCallException
      */
     public function add($child, $type = null, array $options = [])
@@ -94,10 +91,6 @@ public function add($child, $type = null, array $options = [])
      *
      * This method should not be invoked.
      *
-     * @param string                   $name
-     * @param string|FormTypeInterface $type
-     * @param array                    $options
-     *
      * @throws BadMethodCallException
      */
     public function create($name, $type = null, array $options = [])
diff --git a/src/Symfony/Component/Form/Form.php b/src/Symfony/Component/Form/Form.php
index aadab4d752284..e7691cdbc1b40 100644
--- a/src/Symfony/Component/Form/Form.php
+++ b/src/Symfony/Component/Form/Form.php
@@ -849,8 +849,8 @@ public function add($child, $type = null, array $options = [])
 
             $child = (string) $child;
 
-            if (null !== $type && !\is_string($type) && !$type instanceof FormTypeInterface) {
-                throw new UnexpectedTypeException($type, 'string or Symfony\Component\Form\FormTypeInterface');
+            if (null !== $type && !\is_string($type)) {
+                throw new UnexpectedTypeException($type, 'string or null');
             }
 
             // Never initialize child forms automatically
diff --git a/src/Symfony/Component/Form/FormBuilder.php b/src/Symfony/Component/Form/FormBuilder.php
index 6b6a1728b2190..87b4485a6f11b 100644
--- a/src/Symfony/Component/Form/FormBuilder.php
+++ b/src/Symfony/Component/Form/FormBuilder.php
@@ -66,8 +66,8 @@ public function add($child, $type = null, array $options = [])
             throw new UnexpectedTypeException($child, 'string or Symfony\Component\Form\FormBuilderInterface');
         }
 
-        if (null !== $type && !\is_string($type) && !$type instanceof FormTypeInterface) {
-            throw new UnexpectedTypeException($type, 'string or Symfony\Component\Form\FormTypeInterface');
+        if (null !== $type && !\is_string($type)) {
+            throw new UnexpectedTypeException($type, 'string or null');
         }
 
         // Add to "children" to maintain order
diff --git a/src/Symfony/Component/Form/Tests/FormBuilderTest.php b/src/Symfony/Component/Form/Tests/FormBuilderTest.php
index 38d29a28d8132..d831e0f3f2958 100644
--- a/src/Symfony/Component/Form/Tests/FormBuilderTest.php
+++ b/src/Symfony/Component/Form/Tests/FormBuilderTest.php
@@ -120,13 +120,6 @@ public function testMaintainOrderOfLazyAndExplicitChildren()
         $this->assertSame(['foo', 'bar', 'baz'], array_keys($children));
     }
 
-    public function testAddFormType()
-    {
-        $this->assertFalse($this->builder->has('foo'));
-        $this->builder->add('foo', $this->getMockBuilder('Symfony\Component\Form\FormTypeInterface')->getMock());
-        $this->assertTrue($this->builder->has('foo'));
-    }
-
     public function testRemove()
     {
         $this->builder->add('foo', 'Symfony\Component\Form\Extension\Core\Type\TextType');