diff --git a/tests/CollectionTest.php b/tests/CollectionTest.php
index da44b6a..9d55033 100644
--- a/tests/CollectionTest.php
+++ b/tests/CollectionTest.php
@@ -35,7 +35,7 @@ public function testExceptionOnInvalidEncoding()
      *
      * @return array
      */
-    public function mrcFiles()
+    public static function mrcFiles()
     {
         return [
             ['sandburg.mrc', 1],        // Single binary MARC file
@@ -48,7 +48,7 @@ public function mrcFiles()
      *
      * @return array
      */
-    public function xmlFiles()
+    public static function xmlFiles()
     {
         return [
             ['oaipmh-bibsys.xml', 89],  // Records encapsulated in OAI-PMH response