diff --git a/src/Query/Query.php b/src/Query/Query.php
index cef2f67..265e130 100644
--- a/src/Query/Query.php
+++ b/src/Query/Query.php
@@ -417,7 +417,7 @@ class Query implements QueryInterface {
   public function __sleep() {
     $this->indexId = $this->index->id();
     $keys = get_object_vars($this);
-    unset($keys['index']);
+    unset($keys['index'], $keys['resultsCache'], $keys['stringTranslation']);
     return array_keys($keys);
   }
 
diff --git a/src/Tests/IntegrationTest.php b/src/Tests/IntegrationTest.php
index c6f177e..197af4b 100644
--- a/src/Tests/IntegrationTest.php
+++ b/src/Tests/IntegrationTest.php
@@ -165,6 +165,9 @@ class IntegrationTest extends WebTestBase {
       throw new SearchApiException();
     }
 
+    // Verify that search queries can be serialized.
+    serialize($index->query());
+
     // Test the "Save and edit" button.
     $index2_id = 'test_index2';
     $edit['id'] = $index2_id;