diff --git a/Test/Export/AbstractAggregatorTest.php b/Test/Export/AbstractAggregatorTest.php
index d7623788b..c03fecfc6 100644
--- a/Test/Export/AbstractAggregatorTest.php
+++ b/Test/Export/AbstractAggregatorTest.php
@@ -129,6 +129,8 @@ abstract class AbstractAggregatorTest extends KernelTestCase
     {
         $queryKeys = $this->getAggregator()->getQueryKeys($data);
         
+        $this->assertInternalType('array', $queryKeys,
+            "test that the query keys returned are an array");
         $this->assertContainsOnly("string", $queryKeys,
             "test that the query keys returned by `getQueryKeys` are only strings");
         $this->assertGreaterThanOrEqual(1, count($queryKeys),