diff --git a/lib/eslint/eslint.js b/lib/eslint/eslint.js
index b4a28b2905d..196ce8d7bd5 100644
--- a/lib/eslint/eslint.js
+++ b/lib/eslint/eslint.js
@@ -80,10 +80,22 @@ const { CLIEngine } = require("../cli-engine");
  * @property {(results: LintResult[]) => string} format The main formatter method.
  */
 
+/**
+ * Private properties for the `ESLint` instance.
+ * @typedef {Object} LinterInternalSlots
+ * @property {CLIEngine} cliEngine The wrapped CLIEngine instance.
+ */
+
 //------------------------------------------------------------------------------
 // Helpers
 //------------------------------------------------------------------------------
 
+/**
+ * The map with which to store private properties.
+ * @type {WeakMap<ESLint, ESLintInternalSlots>}
+ */
+const internalSlotsMap = new WeakMap();
+
 /**
  * Normalizes an array of plugins to their respective IDs.
  * @param {string[]|PluginElement[]} plugins An array of plugins to normalize.
@@ -283,17 +295,22 @@ class ESLint {
      * @param {ESLintOptions} options The options for this instance.
      */
     constructor(options) {
-        this._cliEngine = new CLIEngine(processOptions(options));
+        const cliEngine = new CLIEngine(processOptions(options));
 
         if (options.plugins.length) {
             for (const plugin of options.plugins) {
-                if (typeof plugin === "object" && plugin !== null) {
-                    this._cliEngine.addPlugin(plugin.id, plugin.definition);
+                if (typeof plugin === "object" && !Array.isArray(plugin) && plugin !== null) {
+                    cliEngine.addPlugin(plugin.id, plugin.definition);
                 } else if (typeof plugin !== "string") {
                     throw new Error("Invalid plugin. Plugins must be specified as a string (e.g., \"eslint-plugin-example\") or as an object (e.g., { id: string; definition: Object }).");
                 }
             }
         }
+
+        // Initialize private properties.
+        internalSlotsMap.set(this, {
+            cliEngine
+        });
     }
 
     /**
@@ -338,7 +355,9 @@ class ESLint {
      * @returns {Promise<LintResult[]>} The results of linting the file patterns given.
      */
     async lintFiles(patterns) {
-        return processCLIEngineLintReport(this._cliEngine.executeOnFiles(patterns));
+        const { cliEngine } = internalSlotsMap.get(this);
+
+        return processCLIEngineLintReport(cliEngine.executeOnFiles(patterns));
     }
 
     /**
@@ -350,7 +369,9 @@ class ESLint {
      * @returns {Promise<LintResult[]>} The results of linting the string of code given.
      */
     async lintText(code, { filePath = null, warnIgnored = false }) {
-        return processCLIEngineLintReport(this._cliEngine.executeOnText(code, filePath, warnIgnored));
+        const { cliEngine } = internalSlotsMap.get(this);
+
+        return processCLIEngineLintReport(cliEngine.executeOnText(code, filePath, warnIgnored));
     }
 
     /**
@@ -361,7 +382,8 @@ class ESLint {
      * @returns {Promise<Formatter|null>} A promise resolving to the formatter object or null if not found.
      */
     async loadFormatter(name) {
-        const formatter = this._cliEngine.getFormatter(name);
+        const { cliEngine } = internalSlotsMap.get(this);
+        const formatter = cliEngine.getFormatter(name);
 
         if (formatter === null) {
             return null;
@@ -382,7 +404,7 @@ class ESLint {
                 return formatter(results, {
                     get rulesMeta() {
                         if (!rulesMeta) {
-                            rulesMeta = createRulesMeta(this._cliEngine.getRules());
+                            rulesMeta = createRulesMeta(cliEngine.getRules());
                         }
 
                         return rulesMeta;
@@ -400,7 +422,9 @@ class ESLint {
      * @returns {Promise<ConfigData>} A configuration object for the file.
      */
     async calculateConfigForFile(filePath) {
-        return this._cliEngine.getConfigForFile(filePath);
+        const { cliEngine } = internalSlotsMap.get(this);
+
+        return cliEngine.getConfigForFile(filePath);
     }
 
     /**
@@ -409,7 +433,9 @@ class ESLint {
      * @returns {boolean} Whether or not the given path is ignored.
      */
     async isPathIgnored(filePath) {
-        return this._cliEngine.isPathIgnored(filePath);
+        const { cliEngine } = internalSlotsMap.get(this);
+
+        return cliEngine.isPathIgnored(filePath);
     }
 }