diff --git a/tests/Arch.php b/tests/Arch.php
index f69c58df..44d49004 100644
--- a/tests/Arch.php
+++ b/tests/Arch.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Pest\Expectation;
 use Pest\Plugins\Tia\BaselineSync;
 
diff --git a/tests/Features/AfterAll.php b/tests/Features/AfterAll.php
index 78401f08..6ef10fff 100644
--- a/tests/Features/AfterAll.php
+++ b/tests/Features/AfterAll.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 $file = __DIR__.DIRECTORY_SEPARATOR.'after-all-test';
 
 beforeAll(function () use ($file): void {
diff --git a/tests/Features/BeforeEachProxiesToTestCallWithExpectations.php b/tests/Features/BeforeEachProxiesToTestCallWithExpectations.php
index 98037eea..3c70c32e 100644
--- a/tests/Features/BeforeEachProxiesToTestCallWithExpectations.php
+++ b/tests/Features/BeforeEachProxiesToTestCallWithExpectations.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 beforeEach()->expect(true)->toBeTrue();
 
 test('runs 1', function (): void {
diff --git a/tests/Features/BeforeEachProxiesToTestCallWithSkip.php b/tests/Features/BeforeEachProxiesToTestCallWithSkip.php
index 34cc61fb..bbeee085 100644
--- a/tests/Features/BeforeEachProxiesToTestCallWithSkip.php
+++ b/tests/Features/BeforeEachProxiesToTestCallWithSkip.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 beforeEach()->skip();
 
 test('does not run 1', function (): void {
diff --git a/tests/Features/Expect/toBeIntBackedEnum.php b/tests/Features/Expect/toBeIntBackedEnum.php
index 10ee86c7..d140944b 100644
--- a/tests/Features/Expect/toBeIntBackedEnum.php
+++ b/tests/Features/Expect/toBeIntBackedEnum.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 test('enum is backed by int')
     ->expect('Tests\Fixtures\Arch\ToBeIntBackedEnum\HasIntBacking')
     ->toBeIntBackedEnum();
diff --git a/tests/Features/Expect/toBeStringBackedEnum.php b/tests/Features/Expect/toBeStringBackedEnum.php
index 4451185d..2d9ad041 100644
--- a/tests/Features/Expect/toBeStringBackedEnum.php
+++ b/tests/Features/Expect/toBeStringBackedEnum.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 test('enum is backed by string')
     ->expect('Tests\Fixtures\Arch\ToBeStringBackedEnum\HasStringBacking')
     ->toBeStringBackedEnum();
diff --git a/tests/Features/Expect/toHaveAttribute.php b/tests/Features/Expect/toHaveAttribute.php
index b94a2fc4..31234fe5 100644
--- a/tests/Features/Expect/toHaveAttribute.php
+++ b/tests/Features/Expect/toHaveAttribute.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Pest\Arch\Exceptions\ArchExpectationFailedException;
 use Tests\Fixtures\Arch\ToHaveAttribute\Attributes\AsAttribute;
 
diff --git a/tests/Features/Expect/toHaveKey.php b/tests/Features/Expect/toHaveKey.php
index 94f837c5..34063559 100644
--- a/tests/Features/Expect/toHaveKey.php
+++ b/tests/Features/Expect/toHaveKey.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PHPUnit\Framework\ExpectationFailedException;
 
 $test_array = [
diff --git a/tests/Features/Expect/toHavePrefix.php b/tests/Features/Expect/toHavePrefix.php
index eea734ae..70e0d8fc 100644
--- a/tests/Features/Expect/toHavePrefix.php
+++ b/tests/Features/Expect/toHavePrefix.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Pest\Arch\Exceptions\ArchExpectationFailedException;
 
 test('missing prefix')
diff --git a/tests/Features/Expect/toHaveSuffix.php b/tests/Features/Expect/toHaveSuffix.php
index 766c9e54..bd6977f9 100644
--- a/tests/Features/Expect/toHaveSuffix.php
+++ b/tests/Features/Expect/toHaveSuffix.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Pest\Arch\Exceptions\ArchExpectationFailedException;
 
 test('missing suffix')
diff --git a/tests/Features/Fail.php b/tests/Features/Fail.php
index 7bf0727a..ccc8bf91 100644
--- a/tests/Features/Fail.php
+++ b/tests/Features/Fail.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PHPUnit\Framework\AssertionFailedError;
 
 it('may fail', function (): void {
diff --git a/tests/Features/Fails.php b/tests/Features/Fails.php
index f60f3292..006e2fae 100644
--- a/tests/Features/Fails.php
+++ b/tests/Features/Fails.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 it('may fail', function (): void {
     $this->fail();
 })->fails();
diff --git a/tests/Features/Test.php b/tests/Features/Test.php
index b0a4aad7..a14ba486 100644
--- a/tests/Features/Test.php
+++ b/tests/Features/Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 test('a test', function (): void {
     $this->assertArrayHasKey('key', ['key' => 'foo']);
 });
diff --git a/tests/Unit/Plugins/Tia/ContentHash.php b/tests/Unit/Plugins/Tia/ContentHash.php
index f81f3edb..e5af75a8 100644
--- a/tests/Unit/Plugins/Tia/ContentHash.php
+++ b/tests/Unit/Plugins/Tia/ContentHash.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Pest\Plugins\Tia\ContentHash;
 
 describe('of()', function (): void {