diff --git a/lib/cartodb/models/mapconfig/adapter/mapconfig-overviews-adapter.js b/lib/cartodb/models/mapconfig/adapter/mapconfig-overviews-adapter.js
index a104c592..e67a2513 100644
--- a/lib/cartodb/models/mapconfig/adapter/mapconfig-overviews-adapter.js
+++ b/lib/cartodb/models/mapconfig/adapter/mapconfig-overviews-adapter.js
@@ -1,4 +1,3 @@
-var step = require('step');
 var queue = require('queue-async');
 var _ = require('underscore');
 
@@ -9,93 +8,119 @@ function MapConfigOverviewsAdapter(overviewsMetadataBackend, filterStatsBackend)
 
 module.exports = MapConfigOverviewsAdapter;
 
-MapConfigOverviewsAdapter.prototype.getMapConfig = function(user, requestMapConfig, params, context, callback) {
-  var self = this;
-
-  var layers = requestMapConfig.layers;
-  var analysesResults = context.analysesResults;
-
-  if (!layers || layers.length === 0) {
-      return callback(null, requestMapConfig);
-  }
-
-  var augmentLayersQueue = queue(layers.length);
-
-  function augmentLayer(layer, done) {
-      if ( layer.type !== 'mapnik' && layer.type !== 'cartodb' ) {
-          return done(null, layer);
-      }
-      self.overviewsMetadataBackend.getOverviewsMetadata(user, layer.options.sql, function(err, metadata){
-           if (err) {
-               done(err, layer);
-           } else {
-               var query_rewrite_data = { overviews: metadata };
-               step(
-                   function collectFiltersData() {
-                       var filters, unfiltered_query;
-                       if ( layer.options.source && analysesResults && !layer.options.sql_wrap) {
-                           var sourceId = layer.options.source.id;
-                           var node = _.find(analysesResults, function(a){ return a.rootNode.params.id === sourceId; });
-                           if ( node ) {
-                               node = node.rootNode;
-                               filters = node.getFilters();
-                               var filters_disabler = Object.keys(filters).reduce(
-                                   function(disabler, filter_id){ disabler[filter_id] = false; return disabler; },
-                                   {}
-                               );
-                               unfiltered_query = node.getQuery(filters_disabler);
-                               query_rewrite_data.filters = filters;
-                               query_rewrite_data.unfiltered_query = unfiltered_query;
-                           }
-                       }
-                       this(null, filters, unfiltered_query);
-                   },
-                   function collectStatsData(err, filters, unfiltered_query) {
-                       var next_step = this;
-                       if ( filters ) {
-                           self.filterStatsBackend.getFilterStats(
-                               user,
-                               unfiltered_query, filters,
-                               function(err, stats) {
-                                 if ( !err ) {
-                                     query_rewrite_data.filter_stats = stats;
-                                 }
-                                 return next_step(err);
-                               }
-                           );
-                       } else {
-                           return next_step(null);
-                       }
-                   },
-                   function addDataToLayer(err) {
-                       if ( !err && !_.isEmpty(metadata) ) {
-                           layer = _.extend({}, layer);
-                           layer.options = _.extend({}, layer.options, { query_rewrite_data: query_rewrite_data });
-                       }
-                       done(null, layer);
-                   }
-               );
-           }
-      });
-  }
-
-  function layersAugmentQueueFinish(err, layers) {
-    if (err) {
-        return callback(err);
-    }
+MapConfigOverviewsAdapter.prototype.getMapConfig = function (user, requestMapConfig, params, context, callback) {
+    var layers = requestMapConfig.layers;
+    var analysesResults = context.analysesResults;
 
     if (!layers || layers.length === 0) {
-        return callback(new Error('Missing layers array from layergroup config'));
+        return callback(null, requestMapConfig);
     }
 
-    requestMapConfig.layers = layers;
+    var augmentLayersQueue = queue(layers.length);
 
-    return callback(null, requestMapConfig);
-  }
+    layers.forEach(layer => augmentLayersQueue.defer(this._augmentLayer.bind(this), user, layer, analysesResults));
 
-  layers.forEach(function(layer) {
-      augmentLayersQueue.defer(augmentLayer, layer);
-  });
-  augmentLayersQueue.awaitAll(layersAugmentQueueFinish);
+    augmentLayersQueue.awaitAll(function layersAugmentQueueFinish (err, layers) {
+        if (err) {
+            return callback(err);
+        }
 
+        if (!layers || layers.length === 0) {
+            return callback(new Error('Missing layers array from layergroup config'));
+        }
+
+        requestMapConfig.layers = layers;
+
+        return callback(null, requestMapConfig);
+    });
 };
+
+MapConfigOverviewsAdapter.prototype._augmentLayer = function (user, layer, analysesResults, callback) {
+    if (layer.type !== 'mapnik' && layer.type !== 'cartodb') {
+        return callback(null, layer);
+    }
+
+    this.overviewsMetadataBackend.getOverviewsMetadata(user, layer.options.sql, (err, metadata) => {
+        if (err) {
+            return callback(err, layer);
+        }
+
+        if (_.isEmpty(metadata)) {
+            return callback(null, layer);
+        }
+
+        var filters = getFilters(analysesResults, layer);
+
+        if (!filters) {
+            layer.options = Object.assign({}, layer.options, getQueryRewriteData(layer, analysesResults, {
+                overviews: metadata
+            }));
+
+            return callback(null, layer);
+        }
+
+        var unfilteredQuery = getUnfilteredQuery(analysesResults, layer);
+
+        this.filterStatsBackend.getFilterStats(user, unfilteredQuery, filters, function (err, stats) {
+            if (err) {
+                return callback(null, layer);
+            }
+
+            layer.options = Object.assign({}, layer.options, getQueryRewriteData(layer, analysesResults, {
+                overviews: metadata,
+                filter_stats: stats
+            }));
+
+            return callback(null, layer);
+        });
+    });
+};
+
+function getRootNode (analysesResults, sourceId) {
+    var node = _.find(analysesResults, function (a) {
+        return a.rootNode.params.id === sourceId;
+    });
+
+    return node ? node.rootNode : undefined;
+}
+
+function getFilters (analysesResults, layer) {
+    if (layer.options.source && analysesResults && !layer.options.sql_wrap) {
+        var sourceId = layer.options.source.id;
+        var node = getRootNode(analysesResults, sourceId);
+
+        if (node) {
+            return node.getFilters();
+        }
+    }
+}
+
+function getUnfilteredQuery (analysesResults, layer) {
+    if (layer.options.source && analysesResults && !layer.options.sql_wrap) {
+        var sourceId = layer.options.source.id;
+        var node = getRootNode(analysesResults, sourceId);
+
+        if (node) {
+            var filters = node.getFilters();
+            var filters_disabler = Object.keys(filters).reduce(function (disabler, filter_id) {
+                disabler[filter_id] = false;
+                return disabler;
+            }, {});
+
+            return node.getQuery(filters_disabler);
+        }
+    }
+}
+
+function getQueryRewriteData (layer, analysesResults, extend = {}) {
+    var queryRewriteData = {};
+
+    if (layer.options.source && analysesResults && !layer.options.sql_wrap) {
+        queryRewriteData.filters = getFilters(analysesResults, layer);
+        queryRewriteData.unfiltered_query = getUnfilteredQuery(analysesResults, layer);
+    }
+
+    queryRewriteData = Object.assign({}, queryRewriteData, extend);
+
+    return { query_rewrite_data: queryRewriteData };
+}