diff --git a/backend/tests/pipeline_test.rs b/backend/tests/pipeline_test.rs
index 11413f9..8bf552e 100644
--- a/backend/tests/pipeline_test.rs
+++ b/backend/tests/pipeline_test.rs
@@ -634,7 +634,7 @@ async fn preferred_sources_processed_first() {
     assert!(status_b.is_success(), "Source B creation should succeed");
 
     // Mark source A as preferred
-    let pref_body = serde_json::json!({ "source_ids": [source_a_id] });
+    let pref_body = serde_json::json!({ "source_ids": [source_a_id], "theme_id": theme_id });
     let (pref_status, _) = app
         .put_with_session("/api/v1/sources/preferred", &pref_body, &session)
         .await;