diff --git a/tests/ResultTest.php b/tests/ResultTest.php
index a6a79a4..80321b1 100644
--- a/tests/ResultTest.php
+++ b/tests/ResultTest.php
@@ -14,7 +14,7 @@ public function testCountable(): void
         $this->assertSame(0, count($result));
     }
 
-    public function testIterator()
+    public function testIterator(): void
     {
         $result = new Result([['column' => 'value']]);
         $this->assertSame(1, count($result));