diff --git a/x-pack/legacy/plugins/ml/server/models/bucket_span_estimator/__tests__/bucket_span_estimator.js b/x-pack/legacy/plugins/ml/server/models/bucket_span_estimator/__tests__/bucket_span_estimator.js
deleted file mode 100644
index c003d3117132f..0000000000000
--- a/x-pack/legacy/plugins/ml/server/models/bucket_span_estimator/__tests__/bucket_span_estimator.js
+++ /dev/null
@@ -1,137 +0,0 @@
-/*
- * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
- * or more contributor license agreements. Licensed under the Elastic License;
- * you may not use this file except in compliance with the Elastic License.
- */
-
-import sinon from 'sinon';
-import expect from '@kbn/expect';
-import { estimateBucketSpanFactory } from '../bucket_span_estimator';
-
-// Mock callWithRequest with the ability to simulate returning different
-// permission settings. On each call using `ml.privilegeCheck` we retrieve
-// the last value from `permissions` and pass that to one of the permission
-// settings. The tests call `ml.privilegeCheck` two times, the first time
-// sufficient permissions should be returned, the second time insufficient
-// permissions.
-const permissions = [false, true];
-const callWithRequest = method => {
-  return new Promise(resolve => {
-    if (method === 'ml.privilegeCheck') {
-      resolve({
-        cluster: {
-          'cluster:monitor/xpack/ml/job/get': true,
-          'cluster:monitor/xpack/ml/job/stats/get': true,
-          'cluster:monitor/xpack/ml/datafeeds/get': true,
-          'cluster:monitor/xpack/ml/datafeeds/stats/get': permissions.pop(),
-        },
-      });
-      return;
-    }
-    resolve({});
-  });
-};
-
-// mock callWithInternalUserFactory
-// we replace the return value of the factory with the above mocked callWithRequest
-import * as mockModule from '../../../client/call_with_internal_user_factory';
-
-// mock xpack_main plugin
-function mockXpackMainPluginFactory(isEnabled = false, licenseType = 'platinum') {
-  return {
-    info: {
-      isAvailable: () => true,
-      feature: () => ({
-        isEnabled: () => isEnabled,
-      }),
-      license: {
-        getType: () => licenseType,
-      },
-    },
-  };
-}
-
-const mockElasticsearchPlugin = {};
-// mock configuration to be passed to the estimator
-const formConfig = {
-  aggTypes: ['count'],
-  duration: {},
-  fields: [null],
-  index: '',
-  query: {
-    bool: {
-      must: [{ match_all: {} }],
-      must_not: [],
-    },
-  },
-};
-
-describe('ML - BucketSpanEstimator', () => {
-  let mockCallWithInternalUserFactory;
-
-  beforeEach(() => {
-    mockCallWithInternalUserFactory = sinon.mock(mockModule);
-    mockCallWithInternalUserFactory
-      .expects('callWithInternalUserFactory')
-      .once()
-      .returns(callWithRequest);
-  });
-
-  it('call factory', () => {
-    expect(function() {
-      estimateBucketSpanFactory(callWithRequest);
-      mockCallWithInternalUserFactory.verify();
-    }).to.not.throwError('Not initialized.');
-  });
-
-  it('call factory and estimator with security disabled', done => {
-    expect(function() {
-      const estimateBucketSpan = estimateBucketSpanFactory(
-        callWithRequest,
-        mockElasticsearchPlugin,
-        mockXpackMainPluginFactory()
-      );
-
-      estimateBucketSpan(formConfig).catch(catchData => {
-        expect(catchData).to.be('Unable to retrieve cluster setting search.max_buckets');
-        mockCallWithInternalUserFactory.verify();
-        done();
-      });
-    }).to.not.throwError('Not initialized.');
-  });
-
-  it('call factory and estimator with security enabled and sufficient permissions.', done => {
-    expect(function() {
-      const estimateBucketSpan = estimateBucketSpanFactory(
-        callWithRequest,
-        mockElasticsearchPlugin,
-        mockXpackMainPluginFactory(true)
-      );
-      estimateBucketSpan(formConfig).catch(catchData => {
-        expect(catchData).to.be('Unable to retrieve cluster setting search.max_buckets');
-        mockCallWithInternalUserFactory.verify();
-        done();
-      });
-    }).to.not.throwError('Not initialized.');
-  });
-
-  it('call factory and estimator with security enabled and insufficient permissions.', done => {
-    expect(function() {
-      const estimateBucketSpan = estimateBucketSpanFactory(
-        callWithRequest,
-        mockElasticsearchPlugin,
-        mockXpackMainPluginFactory(true)
-      );
-
-      estimateBucketSpan(formConfig).catch(catchData => {
-        expect(catchData).to.be('Insufficient permissions to call bucket span estimation.');
-        mockCallWithInternalUserFactory.verify();
-        done();
-      });
-    }).to.not.throwError('Not initialized.');
-  });
-
-  afterEach(() => {
-    mockCallWithInternalUserFactory.restore();
-  });
-});
diff --git a/x-pack/legacy/plugins/ml/server/models/bucket_span_estimator/bucket_span_estimator.js b/x-pack/legacy/plugins/ml/server/models/bucket_span_estimator/bucket_span_estimator.js
index c0edcb5eeb537..8c9e0a9421701 100644
--- a/x-pack/legacy/plugins/ml/server/models/bucket_span_estimator/bucket_span_estimator.js
+++ b/x-pack/legacy/plugins/ml/server/models/bucket_span_estimator/bucket_span_estimator.js
@@ -343,11 +343,21 @@ export function estimateBucketSpanFactory(callWithRequest, elasticsearchPlugin,
           filterPath: '*.*max_buckets',
         })
           .then(settings => {
-            if (typeof settings !== 'object' || typeof settings.defaults !== 'object') {
+            if (typeof settings !== 'object') {
+              reject('Unable to retrieve cluster settings');
+            }
+
+            // search.max_buckets could exist in default, persistent or transient cluster settings
+            const maxBucketsSetting = (settings.defaults ||
+              settings.persistent ||
+              settings.transient ||
+              {})['search.max_buckets'];
+
+            if (maxBucketsSetting === undefined) {
               reject('Unable to retrieve cluster setting search.max_buckets');
             }
 
-            const maxBuckets = parseInt(settings.defaults['search.max_buckets']);
+            const maxBuckets = parseInt(maxBucketsSetting);
 
             const runEstimator = (splitFieldValues = []) => {
               const bucketSpanEstimator = new BucketSpanEstimator(