diff --git a/backend/src/handlers/sources.rs b/backend/src/handlers/sources.rs
index 0c276f7..67e38ab 100644
--- a/backend/src/handlers/sources.rs
+++ b/backend/src/handlers/sources.rs
@@ -324,5 +324,5 @@ pub async fn update_preferred(
     }
 
     db::sources::update_preferred(&state.pool, auth_user.id, &body.source_ids, body.theme_id).await?;
-    Ok(StatusCode::OK)
+    Ok(StatusCode::NO_CONTENT)
 }
diff --git a/backend/tests/api_sources_preferred_test.rs b/backend/tests/api_sources_preferred_test.rs
index e1aa8e4..b2f9f62 100644
--- a/backend/tests/api_sources_preferred_test.rs
+++ b/backend/tests/api_sources_preferred_test.rs
@@ -62,7 +62,7 @@ async fn update_preferred_sets_sources() {
     let (pref_status, _) = app
         .put_with_session("/api/v1/sources/preferred", &pref_body, &session)
         .await;
-    assert_eq!(pref_status, StatusCode::OK);
+    assert_eq!(pref_status, StatusCode::NO_CONTENT);
 
     // GET /sources → verify preferred flags
     let (list_status, list_body) = app
@@ -132,7 +132,7 @@ async fn update_preferred_clears_all_when_empty() {
     let (pref_status, _) = app
         .put_with_session("/api/v1/sources/preferred", &pref_body, &session)
         .await;
-    assert_eq!(pref_status, StatusCode::OK);
+    assert_eq!(pref_status, StatusCode::NO_CONTENT);
 
     // Clear all preferred
     let clear_body = serde_json::json!({
diff --git a/backend/tests/pipeline_test.rs b/backend/tests/pipeline_test.rs
index 8bf552e..a6ed0a1 100644
--- a/backend/tests/pipeline_test.rs
+++ b/backend/tests/pipeline_test.rs
@@ -638,7 +638,7 @@ async fn preferred_sources_processed_first() {
     let (pref_status, _) = app
         .put_with_session("/api/v1/sources/preferred", &pref_body, &session)
         .await;
-    assert_eq!(pref_status.as_u16(), 200, "Setting preferred sources should succeed");
+    assert_eq!(pref_status.as_u16(), 204, "Setting preferred sources should succeed");
 
     // Run the pipeline
     let mock_provider = MockLlmProvider::new()
diff --git a/e2e/tests/sources.spec.ts b/e2e/tests/sources.spec.ts
index 6ac050f..3f4f01f 100644
--- a/e2e/tests/sources.spec.ts
+++ b/e2e/tests/sources.spec.ts
@@ -132,7 +132,7 @@ test.describe('Sources management', () => {
       });
       return { status: resp.status };
     }, { ids: [sourceId2], tid: themeId });
-    expect(prefResp.status).toBe(200);
+    expect(prefResp.status).toBe(204);
 
     // Step 9: Verify source is now preferred
     const listResp3 = await page.evaluate(async (tid: string) => {