diff --git a/README.md b/README.md
index 1a87e31..67dc47f 100644
--- a/README.md
+++ b/README.md
@@ -41,7 +41,7 @@ The following set of extra asserts are provided by this package:
 - [Iso3166Country](#iso3166country) (requires `isoc`)
 - [Json](#json)
 - [NotEmpty](#notempty)
-- [NullOrDate](#nullordate)
+- [NullOrDate](#nullordate) (requires `moment` for format validation only)
 - [NullOrString](#nullorstring)
 - [Phone](#phone) (requires `google-libphonenumber`)
 - [PlainObject](#plainobject)
@@ -152,8 +152,14 @@ Tests if the value is valid json.
 ### NotEmpty
 Tests if the value is not an empty (empty object, empty array, empty string, etc).
 
+### NullOrDate
+Tests if the value is `null` or a valid date.
+
+#### Arguments
+- `format` (optional) - the format in which the date must be in.
+
 ### NullOrString
-Tests if the value is a `null` or `string`, optionally within some boundaries.
+Tests if the value is `null` or a string, optionally within some boundaries.
 
 #### Arguments
 - `boundaries` (optional) - `max` and/or `min` boundaries to test the string for.
diff --git a/src/asserts/date-assert.js b/src/asserts/date-assert.js
index 97743ee..4c65eaa 100644
--- a/src/asserts/date-assert.js
+++ b/src/asserts/date-assert.js
@@ -50,15 +50,15 @@ export default function dateAssert({ format } = {}) {
       throw new Violation(this, value, { value: 'must_be_a_date_or_a_string' });
     }
 
-    if (isNaN(Date.parse(value)) === true) {
-      throw new Violation(this, value);
-    }
+    if (this.format) {
+      if (!moment(value, this.format, true).isValid()) {
+        throw new Violation(this, value);
+      }
 
-    if (!this.format) {
       return true;
     }
 
-    if (!moment(value, this.format, true).isValid()) {
+    if (isNaN(Date.parse(value)) === true) {
       throw new Violation(this, value);
     }
 
diff --git a/src/asserts/date-diff-greater-than-assert.js b/src/asserts/date-diff-greater-than-assert.js
index 2d3c0bd..9d515c0 100644
--- a/src/asserts/date-diff-greater-than-assert.js
+++ b/src/asserts/date-diff-greater-than-assert.js
@@ -57,7 +57,7 @@ export default function dateDiffGreaterThanAssert(threshold, options) {
       throw new Violation(this, value, { value: 'must_be_a_date_or_a_string' });
     }
 
-    if (isNaN(Date.parse(value)) === true) {
+    if (!moment(value).isValid()) {
       throw new Violation(this, value, { absolute: this.absolute, asFloat: this.asFloat, fromDate: this.fromDate, threshold: this.threshold, unit: this.unit });
     }
 
diff --git a/src/asserts/date-diff-less-than-assert.js b/src/asserts/date-diff-less-than-assert.js
index 533c002..2a42418 100644
--- a/src/asserts/date-diff-less-than-assert.js
+++ b/src/asserts/date-diff-less-than-assert.js
@@ -57,7 +57,7 @@ export default function dateDiffLessThanAssert(threshold, options) {
       throw new Violation(this, value, { value: 'must_be_a_date_or_a_string' });
     }
 
-    if (isNaN(Date.parse(value)) === true) {
+    if (!moment(value).isValid()) {
       throw new Violation(this, value, { absolute: this.absolute, asFloat: this.asFloat, fromDate: this.fromDate, threshold: this.threshold, unit: this.unit });
     }
 
diff --git a/src/asserts/null-or-date-assert.js b/src/asserts/null-or-date-assert.js
index 43db5ec..d91cc11 100644
--- a/src/asserts/null-or-date-assert.js
+++ b/src/asserts/null-or-date-assert.js
@@ -4,18 +4,43 @@
  */
 
 import { Violation } from 'validator.js';
+import { isString } from 'lodash';
 
 /**
  * Export `NullOrDateAssert`.
  */
 
-export default function nullOrDateAssert() {
+export default function nullOrDateAssert({ format } = {}) {
   /**
    * Class name.
    */
 
   this.__class__ = 'NullOrDate';
 
+  /**
+   * Optional peer dependency.
+   */
+
+  let moment;
+
+  /**
+   * Validate format.
+   */
+
+  if (format) {
+    if (!isString(format)) {
+      throw new Error(`Unsupported format ${format} given`);
+    }
+
+    moment = require('moment');
+  }
+
+  /**
+   * Format to match the input.
+   */
+
+  this.format = format;
+
   /**
    * Validation algorithm.
    */
@@ -29,6 +54,14 @@ export default function nullOrDateAssert() {
       return true;
     }
 
+    if (this.format) {
+      if (!moment(value, this.format, true).isValid()) {
+        throw new Violation(this, value);
+      }
+
+      return true;
+    }
+
     if (isNaN(Date.parse(value)) === true) {
       throw new Violation(this, value);
     }
diff --git a/test/asserts/date-assert_test.js b/test/asserts/date-assert_test.js
index 0ee7086..00b96a7 100644
--- a/test/asserts/date-assert_test.js
+++ b/test/asserts/date-assert_test.js
@@ -82,15 +82,15 @@ describe('DateAssert', () => {
     }
   });
 
-  it('should accept a `Date`', () => {
+  it('should accept a date', () => {
     new Assert().Date().validate(new Date());
   });
 
   it('should accept a correctly formatted date', () => {
-    new Assert().Date({ format: 'YYYY-MM-DD' }).validate('2000-12-30');
+    new Assert().Date({ format: 'MM/YYYY' }).validate('12/2000');
   });
 
-  it('should accept a `string`', () => {
+  it('should accept a string', () => {
     new Assert().Date().validate('2014-10-16');
   });
 });
diff --git a/test/asserts/null-or-date-assert_test.js b/test/asserts/null-or-date-assert_test.js
index ea2780b..e748a16 100644
--- a/test/asserts/null-or-date-assert_test.js
+++ b/test/asserts/null-or-date-assert_test.js
@@ -35,14 +35,40 @@ describe('NullOrDateAssert', () => {
     });
   });
 
-  it('should throw an error if the input value is not a valid date', () => {
+  it('should throw an error if an invalid format is given', () => {
+    const formats = [[], {}, 123];
+
+    formats.forEach(format => {
+      try {
+        new Assert().NullOrDate({ format }).validate();
+
+        should.fail();
+      } catch (e) {
+        e.should.be.instanceOf(Error);
+        e.message.should.equal(`Unsupported format ${format} given`);
+      }
+    });
+  });
+
+  it('should throw an error if value is not correctly formatted', () => {
     try {
-      new Assert().NullOrDate().validate('2015-99-01');
+      new Assert().NullOrDate({ format: 'YYYY-MM-DD' }).validate('20003112');
 
       should.fail();
     } catch (e) {
       e.should.be.instanceOf(Violation);
-      e.show().value.should.equal('2015-99-01');
+      e.show().assert.should.equal('NullOrDate');
+    }
+  });
+
+  it('should throw an error if value does not pass strict validation', () => {
+    try {
+      new Assert().NullOrDate({ format: 'YYYY-MM-DD' }).validate('2000.12.30');
+
+      should.fail();
+    } catch (e) {
+      e.should.be.instanceOf(Violation);
+      e.show().assert.should.equal('NullOrDate');
     }
   });
 
@@ -64,6 +90,10 @@ describe('NullOrDateAssert', () => {
     new Assert().NullOrDate().validate(new Date());
   });
 
+  it('should accept a correctly formatted date', () => {
+    new Assert().NullOrDate({ format: 'MM/YYYY' }).validate('12/2000');
+  });
+
   it('should accept a string', () => {
     new Assert().NullOrDate().validate('2014-10-16');
   });