diff --git a/tests/Forms/BaseControl.extensionMethod.phpt b/tests/Forms/BaseControl.extensionMethod.phpt
new file mode 100644
index 000000000..1cedbbc4f
--- /dev/null
+++ b/tests/Forms/BaseControl.extensionMethod.phpt
@@ -0,0 +1,36 @@
+<?php
+
+use Nette\Forms\Controls\Button;
+use Nette\Forms\Controls\Checkbox;
+use Nette\Forms\Controls\TextBase;
+use Nette\Forms\Controls\TextInput;
+use Tester\Assert;
+
+
+require __DIR__ . '/../bootstrap.php';
+
+
+TextBase::extensionMethod('test', function ($control, $a, $b) {
+	Assert::type(TextInput::class, $control);
+	Assert::same(1, $a);
+	Assert::same(2, $b);
+	return 'TextInput';
+});
+
+Checkbox::extensionMethod('test', function ($control, $a, $b) {
+	Assert::type(Checkbox::class, $control);
+	Assert::same(1, $a);
+	Assert::same(2, $b);
+	return 'Checkbox';
+});
+
+$control1 = new TextInput;
+Assert::same('TextInput', $control1->test(1, 2));
+
+$control2 = new Checkbox;
+Assert::same('Checkbox', $control2->test(1, 2));
+
+Assert::exception(function () {
+	$control3 = new Button;
+	$control3->test(1, 2);
+}, Nette\MemberAccessException::class);
diff --git a/tests/Forms/Container.extensionMethod.phpt b/tests/Forms/Container.extensionMethod.phpt
new file mode 100644
index 000000000..a0bfcc97d
--- /dev/null
+++ b/tests/Forms/Container.extensionMethod.phpt
@@ -0,0 +1,18 @@
+<?php
+
+use Nette\Forms\Form;
+use Tester\Assert;
+
+
+require __DIR__ . '/../bootstrap.php';
+
+
+Nette\Forms\Container::extensionMethod('test', function ($form, $a, $b) {
+	Assert::type(Nette\Forms\Form::class, $form);
+	Assert::same(1, $a);
+	Assert::same(2, $b);
+	return 3;
+});
+
+$form = new Form;
+Assert::same(3, $form->test(1, 2));