diff --git a/API.md b/API.md
index 2a77fd2e7..dbf568c2d 100755
--- a/API.md
+++ b/API.md
@@ -275,15 +275,6 @@ Creates a new customized instance of the **joi** module where:
 
 Note that the original **joi** module is not modified by this.
 
-### `isExpression(expression)`
-
-Checks whether or not the provided argument is an expression.
-
-```js
-const expression = Joi.x('{a}');
-Joi.isExpression(expression); // returns true
-```
-
 ### `in(ref, [options])`
 
 Creates a [reference](#refkey-options) that when resolved, is used as an array of values to match against the rule, where:
@@ -299,6 +290,23 @@ const schema = Joi.object({
 });
 ```
 
+### `isError(err)`
+
+Checks whether or not the provided argument is a validation error.
+
+```js
+Joi.isError(new Error()); // returns false
+```
+
+### `isExpression(expression)`
+
+Checks whether or not the provided argument is an expression.
+
+```js
+const expression = Joi.x('{a}');
+Joi.isExpression(expression); // returns true
+```
+
 ### `isRef(ref)`
 
 Checks whether or not the provided argument is a reference. Useful if you want to post-process error messages.
diff --git a/lib/annotate.js b/lib/annotate.js
index e96f7ad6d..42798fc3e 100755
--- a/lib/annotate.js
+++ b/lib/annotate.js
@@ -10,23 +10,23 @@ const internals = {
 };
 
 
-exports.error = function (source, stripColorCodes) {
+exports.error = function (stripColorCodes) {
 
-    if (!source._original ||
-        typeof source._original !== 'object') {
+    if (!this._original ||
+        typeof this._original !== 'object') {
 
-        return source.details[0].message;
+        return this.details[0].message;
     }
 
     const redFgEscape = stripColorCodes ? '' : '\u001b[31m';
     const redBgEscape = stripColorCodes ? '' : '\u001b[41m';
     const endColor = stripColorCodes ? '' : '\u001b[0m';
 
-    const obj = Clone(source._original);
+    const obj = Clone(this._original);
 
-    for (let i = source.details.length - 1; i >= 0; --i) {        // Reverse order to process deepest child first
+    for (let i = this.details.length - 1; i >= 0; --i) {        // Reverse order to process deepest child first
         const pos = i + 1;
-        const error = source.details[i];
+        const error = this.details[i];
         const path = error.path;
         let node = obj;
         for (let j = 0; ; ++j) {
@@ -75,9 +75,9 @@ exports.error = function (source, stripColorCodes) {
 
     message = `${message}\n${redFgEscape}`;
 
-    for (let i = 0; i < source.details.length; ++i) {
+    for (let i = 0; i < this.details.length; ++i) {
         const pos = i + 1;
-        message = `${message}\n[${pos}] ${source.details[i].message}`;
+        message = `${message}\n[${pos}] ${this.details[i].message}`;
     }
 
     message = message + endColor;
diff --git a/lib/errors.js b/lib/errors.js
index 92a9bdf8b..0823f924f 100755
--- a/lib/errors.js
+++ b/lib/errors.js
@@ -1,7 +1,5 @@
 'use strict';
 
-const Assert = require('@hapi/hoek/lib/assert');
-
 const Annotate = require('./annotate');
 const Common = require('./common');
 const Template = require('./template');
@@ -243,9 +241,6 @@ exports.details = function (errors, options = {}) {
 
 exports.ValidationError = class extends Error {
 
-    isJoi = true;
-    name = 'ValidationError';
-
     constructor(message, details, original) {
 
         super(message);
@@ -253,9 +248,15 @@ exports.ValidationError = class extends Error {
         this.details = details;
     }
 
-    annotate(stripColorCodes) {
+    static isError(err) {
 
-        Assert(Annotate.error, 'Error annotation is not supported');
-        return Annotate.error(this, stripColorCodes);
+        return err instanceof exports.ValidationError;
     }
 };
+
+
+exports.ValidationError.prototype.isJoi = true;
+
+exports.ValidationError.prototype.name = 'ValidationError';
+
+exports.ValidationError.prototype.annotate = Annotate.error;
diff --git a/lib/index.js b/lib/index.js
index 73b0c2b8b..8813f516d 100755
--- a/lib/index.js
+++ b/lib/index.js
@@ -183,6 +183,7 @@ internals.methods = {
         return joi;
     },
 
+    isError: Errors.ValidationError.isError,
     isExpression: Template.isTemplate,
     isRef: Ref.isRef,
     isSchema: Common.isSchema,
@@ -232,8 +233,7 @@ internals.assert = function (value, schema, annotate, args /* [message], [option
         throw message;
     }
 
-    annotate = annotate && typeof error.annotate === 'function';
-    const display = annotate ? error.annotate() : error.message;
+    const display = annotate && typeof error.annotate === 'function' ? error.annotate() : error.message;
 
     if (error instanceof Errors.ValidationError === false) {
         error = Clone(error);
diff --git a/test/errors.js b/test/errors.js
index 9ffc4e05c..a9b104d6a 100755
--- a/test/errors.js
+++ b/test/errors.js
@@ -21,6 +21,7 @@ describe('errors', () => {
         const err = Joi.valid('foo').validate('bar').error;
         expect(err).to.be.an.error();
         expect(err.isJoi).to.be.true();
+        expect(Joi.isError(err)).to.be.true();
     });