diff --git a/phpstan.neon b/phpstan.neon
index 5ec89139..7e41decb 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -2,3 +2,7 @@ includes:
 	- extension.neon
 	- rules.neon
 	- vendor/phpstan/phpstan-strict-rules/rules.neon
+
+parameters:
+	excludes_analyse:
+		- */tests/*/data/*
diff --git a/tests/Rules/PHPUnit/AssertSameDifferentTypesRuleTest.php b/tests/Rules/PHPUnit/AssertSameDifferentTypesRuleTest.php
new file mode 100644
index 00000000..ac66d1c0
--- /dev/null
+++ b/tests/Rules/PHPUnit/AssertSameDifferentTypesRuleTest.php
@@ -0,0 +1,45 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\PHPUnit;
+
+use PHPStan\Rules\Rule;
+
+class AssertSameDifferentTypesRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new AssertSameDifferentTypesRule();
+	}
+
+	public function testRule()
+	{
+		$this->analyse([__DIR__ . '/data/assert-same.php'], [
+			[
+				'Call to assertSame() with different types string and int will always result in test failure.',
+				10,
+			],
+			[
+				'Call to assertSame() with different types string and stdClass will always result in test failure.',
+				11,
+			],
+			[
+				'Call to assertSame() with different types int and string will always result in test failure.',
+				12,
+			],
+			[
+				'Call to assertSame() with different types string and int will always result in test failure.',
+				13,
+			],
+			[
+				'Call to assertSame() with different types array<int, string> and array<int, int> will always result in test failure.',
+				14,
+			],
+			[
+				'Call to assertSame() with different types array<string> and array<int> will always result in test failure.',
+				35,
+			],
+		]);
+	}
+
+}
diff --git a/tests/Rules/PHPUnit/data/assert-same.php b/tests/Rules/PHPUnit/data/assert-same.php
new file mode 100644
index 00000000..8d3a18c6
--- /dev/null
+++ b/tests/Rules/PHPUnit/data/assert-same.php
@@ -0,0 +1,51 @@
+<?php declare(strict_types = 1);
+
+namespace ExampleTestCase;
+
+class FooTestCase extends \PHPUnit\Framework\TestCase
+{
+
+	public function testObviouslyNotSameAssertSame()
+	{
+		$this->assertSame('1', 1);
+		$this->assertSame('1', new \stdClass());
+		$this->assertSame(1, $this->returnsString());
+		$this->assertSame('1', self::returnsInt());
+		$this->assertSame(['a', 'b'], [1, 2]);
+	}
+
+	private function returnsString(): string
+	{
+		return 'foo';
+	}
+
+	private static function returnsInt(): int
+	{
+		return 1;
+	}
+
+	public function testArrays()
+	{
+		/** @var string[] $a */
+		$a = ['x'];
+
+		/** @var int[] $b */
+		$b = [1, 2];
+
+		$this->assertSame($a, $b);
+	}
+
+	public function testLogicallyCorrectAssertSame()
+	{
+		$this->assertSame(1, 1);
+		$this->assertSame(['a'], ['a', 'b']);
+		$this->assertSame('1', '1');
+		$this->assertSame('1', '2');
+		$this->assertSame(new \stdClass(), new \stdClass());
+		$this->assertSame('1', $this->returnsString());
+		$this->assertSame(1, self::returnsInt());
+		$this->assertSame(['a'], ['a', 1]);
+		$this->assertSame(['a', 2, 3.0], ['a', 1]);
+	}
+
+}
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 22e480dd..9dfa9f56 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,3 +1,7 @@
 <?php declare(strict_types = 1);
 
+use PHPStan\Type\TypeCombinator;
+
 require_once __DIR__ . '/../vendor/autoload.php';
+
+TypeCombinator::setUnionTypesEnabled(true);