diff --git a/lib/include.js b/lib/include.js
index 689ab923..4985ff2a 100644
--- a/lib/include.js
+++ b/lib/include.js
@@ -1,3 +1,7 @@
+var utils = require('./utils');
+var isPlainObject = utils.isPlainObject;
+var defineCachedRelations = utils.defineCachedRelations;
+
 /**
  * Include mixin for ./model.js
  */
@@ -6,16 +10,6 @@ module.exports = Inclusion;
 function Inclusion() {
 }
 
-/*!
- * Check if the argument is plain object
- * @param {*) include The include value
- * @returns {boolean}
- */
-function isObject(include) {
-  return (typeof include === 'object') && (include !== null)
-    && (include.constructor.name === 'Object');
-}
-
 /**
  * Allows you to load relations of several objects and optimize numbers of requests.
  *
@@ -40,7 +34,7 @@ Inclusion.include = function (objects, include, cb) {
 
   if (
     !include || (Array.isArray(include) && include.length === 0) ||
-      (isObject(include) && Object.keys(include).length === 0)
+      (isPlainObject(include) && Object.keys(include).length === 0)
     ) {
     cb(null, objects);
     return;
@@ -58,7 +52,7 @@ Inclusion.include = function (objects, include, cb) {
       nbCallbacks++;
       callback(function () {
         nbCallbacks--;
-        if (nbCallbacks == 0) {
+        if (nbCallbacks === 0) {
           cb(null, objects);
         }
       });
@@ -71,7 +65,7 @@ Inclusion.include = function (objects, include, cb) {
     if (typeof ij === 'string') {
       ij = [ij];
     }
-    if (isObject(ij)) {
+    if (isPlainObject(ij)) {
       var newIj = [];
       for (var key in ij) {
         var obj = {};
@@ -87,7 +81,7 @@ Inclusion.include = function (objects, include, cb) {
     var relations = self.relations;
 
     var relationName, subInclude;
-    if (isObject(include)) {
+    if (isPlainObject(include)) {
       relationName = Object.keys(include)[0];
       subInclude = include[relationName];
     } else {
@@ -100,7 +94,7 @@ Inclusion.include = function (objects, include, cb) {
       return function () {
         cb(new Error('Relation "' + relationName + '" is not defined for '
           + self.modelName + ' model'));
-      }
+      };
     }
 
     var req = {'where': {}};
@@ -138,9 +132,7 @@ Inclusion.include = function (objects, include, cb) {
             delete keysToBeProcessed[objsIncluded[i][relation.keyTo]];
             objectsFrom = objsByKeys[relation.keyFrom][objsIncluded[i][relation.keyTo]];
             for (j = 0; j < objectsFrom.length; j++) {
-              if (!objectsFrom[j].__cachedRelations) {
-                objectsFrom[j].__cachedRelations = {};
-              }
+              defineCachedRelations(objectsFrom[j]);
               if (relation.multiple) {
                 if (!objectsFrom[j].__cachedRelations[relationName]) {
                   objectsFrom[j].__cachedRelations[relationName] = [];
@@ -156,9 +148,7 @@ Inclusion.include = function (objects, include, cb) {
           for (var key in keysToBeProcessed) {
             objectsFrom = objsByKeys[relation.keyFrom][key];
             for (j = 0; j < objectsFrom.length; j++) {
-              if (!objectsFrom[j].__cachedRelations) {
-                objectsFrom[j].__cachedRelations = {};
-              }
+              defineCachedRelations(objectsFrom[j]);
               objectsFrom[j].__cachedRelations[relationName] =
                 relation.multiple ? [] : null;
             }
diff --git a/lib/model.js b/lib/model.js
index 58211b14..dbc23d5f 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -76,8 +76,8 @@ ModelBaseClass.prototype._initProperties = function (data, applySetters) {
     value: {}
   });
 
-  if (data['__cachedRelations']) {
-    this.__cachedRelations = data['__cachedRelations'];
+  if (data.__cachedRelations) {
+    this.__cachedRelations = data.__cachedRelations;
   }
 
   // Check if the strict option is set to false for the model
diff --git a/lib/scope.js b/lib/scope.js
index d37d97c5..a54aad37 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -1,3 +1,5 @@
+var utils = require('./utils');
+var defineCachedRelations = utils.defineCachedRelations;
 /**
  * Module exports
  */
@@ -54,14 +56,12 @@ function defineScope(cls, targetClass, name, params, methods) {
           throw new Error('Method can be only called with one or two arguments');
         }
 
-        if (!this.__cachedRelations || (typeof this.__cachedRelations[name] == 'undefined') || actualRefresh) {
+        if (!this.__cachedRelations || (this.__cachedRelations[name] === undefined) || actualRefresh) {
           var self = this;
           var params = mergeParams(actualCond, caller._scope);
           return targetClass.find(params, function (err, data) {
             if (!err && saveOnCache) {
-              if (!self.__cachedRelations) {
-                self.__cachedRelations = {};
-              }
+              defineCachedRelations(self);
               self.__cachedRelations[name] = data;
             }
             cb(err, data);
diff --git a/lib/utils.js b/lib/utils.js
index 08804dda..520cf462 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -4,6 +4,8 @@ exports.selectFields = selectFields;
 exports.removeUndefined = removeUndefined;
 exports.parseSettings = parseSettings;
 exports.mergeSettings = mergeSettings;
+exports.isPlainObject = isPlainObject;
+exports.defineCachedRelations = defineCachedRelations;
 
 var traverse = require('traverse');
 
@@ -176,4 +178,29 @@ function mergeSettings(target, src) {
   }
 
   return dst;
+}
+
+/**
+ * Define an non-enumerable __cachedRelations property
+ * @param {Object} obj The obj to receive the __cachedRelations
+ */
+function defineCachedRelations(obj) {
+  if (!obj.__cachedRelations) {
+    Object.defineProperty(obj, '__cachedRelations', {
+      writable: true,
+      enumerable: false,
+      configurable: true,
+      value: {}
+    });
+  }
+}
+
+/**
+ * Check if the argument is plain object
+ * @param {*) obj The obj value
+ * @returns {boolean}
+ */
+function isPlainObject(obj) {
+  return (typeof obj === 'object') && (obj !== null)
+    && (obj.constructor === Object);
 }
\ No newline at end of file