diff --git a/tests/ConversionTest.php b/tests/ConversionTest.php
index 7bc812d..d30ffa3 100644
--- a/tests/ConversionTest.php
+++ b/tests/ConversionTest.php
@@ -6,7 +6,7 @@
 
 class ConversionTest extends TestCase
 {
-    public function dataProvider(): array
+    public static function dataProvider(): array
     {
         return array(
             array('', null, ''),