diff --git a/src/test/java/org/opensearch/ad/rest/AnomalyDetectorRestApiIT.java b/src/test/java/org/opensearch/ad/rest/AnomalyDetectorRestApiIT.java
index 65516a241..2deec995f 100644
--- a/src/test/java/org/opensearch/ad/rest/AnomalyDetectorRestApiIT.java
+++ b/src/test/java/org/opensearch/ad/rest/AnomalyDetectorRestApiIT.java
@@ -194,7 +194,7 @@ public void testCreateAnomalyDetectorWithDuplicateName() throws Exception {
             );
     }
 
-    public void testCreateAnomalyDetectorWithFlattenedResultIndex() throws Exception {
+    public void testCreateAnomalyDetector_withFlattenedResultIndex() throws Exception {
         AnomalyDetector detector = createIndexAndGetAnomalyDetector(
             INDEX_NAME,
             ImmutableList.of(TestHelpers.randomFeature("feature_bytes", "agg", true)),
@@ -258,6 +258,80 @@ public void testCreateAnomalyDetectorWithFlattenedResultIndex() throws Exception
         assertTrue("Flattened field 'feature_data_feature_bytes' does not exist", properties.containsKey("feature_data_feature_bytes"));
     }
 
+    public void testUpdateAnomalyDetector_disableFlattenResultIndex_shouldDeletePipeline() throws Exception {
+        AnomalyDetector detector = createIndexAndGetAnomalyDetector(
+            INDEX_NAME,
+            ImmutableList.of(TestHelpers.randomFeature("feature_bytes", "agg", true)),
+            false,
+            true
+        );
+
+        // test behavior when AD is enabled
+        updateClusterSettings(ADEnabledSetting.AD_ENABLED, true);
+        Response response = TestHelpers
+            .makeRequest(client(), "POST", TestHelpers.AD_BASE_DETECTORS_URI, ImmutableMap.of(), TestHelpers.toHttpEntity(detector), null);
+        assertEquals("Create anomaly detector with flattened result index failed", RestStatus.CREATED, TestHelpers.restStatus(response));
+        Map<String, Object> responseMap = entityAsMap(response);
+        String id = (String) responseMap.get("_id");
+        String expectedFlattenedIndex = String
+            .format(Locale.ROOT, "opensearch-ad-plugin-result-test_flattened_%s", id.toLowerCase(Locale.ROOT));
+        String expectedPipelineId = String.format(Locale.ROOT, "flatten_result_index_ingest_pipeline%s", id.toLowerCase(Locale.ROOT));
+        String getIngestPipelineEndpoint = String.format(Locale.ROOT, "_ingest/pipeline/%s", expectedPipelineId);
+        Response getPipelineResponse = TestHelpers.makeRequest(client(), "GET", expectedPipelineId, ImmutableMap.of(), "", null);
+        assertEquals(
+            "Expected 200 response but got: " + getPipelineResponse.getStatusLine().getStatusCode(),
+            200,
+            getPipelineResponse.getStatusLine().getStatusCode()
+        );
+        List<Feature> features = detector.getFeatureAttributes();
+        AnomalyDetector newDetector = new AnomalyDetector(
+            detector.getId(),
+            detector.getVersion(),
+            detector.getName(),
+            detector.getDescription(),
+            detector.getTimeField(),
+            detector.getIndices(),
+            features,
+            detector.getFilterQuery(),
+            detector.getInterval(),
+            detector.getWindowDelay(),
+            detector.getShingleSize(),
+            detector.getUiMetadata(),
+            detector.getSchemaVersion(),
+            detector.getLastUpdateTime(),
+            null,
+            detector.getUser(),
+            detector.getCustomResultIndexOrAlias(),
+            TestHelpers.randomImputationOption(features),
+            randomIntBetween(1, 10000),
+            randomInt(TimeSeriesSettings.MAX_SHINGLE_SIZE / 2),
+            randomIntBetween(1, 1000),
+            null,
+            null,
+            null,
+            null,
+            false,
+            detector.getLastBreakingUIChangeTime()
+        );
+        Response updateResponse = TestHelpers
+            .makeRequest(
+                client(),
+                "PUT",
+                TestHelpers.AD_BASE_DETECTORS_URI + "/" + detector.getId() + "?refresh=true",
+                ImmutableMap.of(),
+                TestHelpers.toHttpEntity(newDetector),
+                null
+            );
+        assertEquals("Update anomaly detector failed", RestStatus.OK, TestHelpers.restStatus(updateResponse));
+        Response getPipelineResponseAfterUpdatingDetector = TestHelpers
+            .makeRequest(client(), "GET", expectedPipelineId, ImmutableMap.of(), "", null);
+        assertEquals(
+            "Expected 404 response but got: " + getPipelineResponseAfterUpdatingDetector.getStatusLine().getStatusCode(),
+            404,
+            getPipelineResponseAfterUpdatingDetector.getStatusLine().getStatusCode()
+        );
+    }
+
     public void testCreateAnomalyDetector() throws Exception {
         AnomalyDetector detector = createIndexAndGetAnomalyDetector(INDEX_NAME);
         updateClusterSettings(ADEnabledSetting.AD_ENABLED, false);