diff --git a/package.json b/package.json
index a011971..edf5ef1 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "description": "JSON Web Token implementation (symmetric and asymmetric)",
   "main": "index.js",
   "scripts": {
-    "test": "mocha --require test/util/fakeDate && nsp check"
+    "test": "mocha --require test/util/fakeDate && nsp check && cost-of-modules"
   },
   "repository": {
     "type": "git",
@@ -19,8 +19,14 @@
     "url": "https://github.com/auth0/node-jsonwebtoken/issues"
   },
   "dependencies": {
-    "joi": "^6.10.1",
     "jws": "^3.1.4",
+    "lodash.includes": "^4.3.0",
+    "lodash.isarray": "^4.0.0",
+    "lodash.isboolean": "^3.0.3",
+    "lodash.isinteger": "^4.0.4",
+    "lodash.isnumber": "^3.0.3",
+    "lodash.isplainobject": "^4.0.6",
+    "lodash.isstring": "^4.0.1",
     "lodash.once": "^4.0.0",
     "ms": "^2.0.0",
     "xtend": "^4.0.1"
@@ -29,6 +35,7 @@
     "atob": "^1.1.2",
     "chai": "^1.10.0",
     "conventional-changelog": "~1.1.0",
+    "cost-of-modules": "^1.0.1",
     "mocha": "^2.1.0",
     "nsp": "^2.6.2",
     "sinon": "^1.15.4"
diff --git a/sign.js b/sign.js
index 38fa78e..370b5d7 100644
--- a/sign.js
+++ b/sign.js
@@ -1,29 +1,53 @@
-var Joi = require('joi');
 var timespan = require('./lib/timespan');
 var xtend = require('xtend');
 var jws = require('jws');
+var includes = require('lodash.includes');
+var isArray = require('lodash.isarray');
+var isBoolean = require('lodash.isboolean');
+var isInteger = require('lodash.isinteger');
+var isNumber = require('lodash.isnumber');
+var isPlainObject = require('lodash.isplainobject');
+var isString = require('lodash.isstring');
 var once = require('lodash.once');
 
-var sign_options_schema = Joi.object().keys({
-  expiresIn: [Joi.number().integer(), Joi.string()],
-  notBefore: [Joi.number().integer(), Joi.string()],
-  audience: [Joi.string(), Joi.array()],
-  algorithm: Joi.string().valid('RS256', 'RS384', 'RS512', 'ES256', 'ES384', 'ES512', 'HS256', 'HS384', 'HS512', 'none'),
-  header: Joi.object(),
-  encoding: Joi.string(),
-  issuer: Joi.string(),
-  subject: Joi.string(),
-  jwtid: Joi.string(),
-  noTimestamp: Joi.boolean(),
-  keyid: Joi.string()
-});
-
-var registered_claims_schema = Joi.object().keys({
-  iat: Joi.number(),
-  exp: Joi.number(),
-  nbf: Joi.number()
-}).unknown();
+var sign_options_schema = {
+  expiresIn: { isValid: function(value) { return isInteger(value) || isString(value); }, message: '"expiresIn" should be a number of seconds or string representing a timespan' },
+  notBefore: { isValid: function(value) { return isInteger(value) || isString(value); }, message: '"notBefore" should be a number of seconds or string representing a timespan' },
+  audience: { isValid: function(value) { return isString(value) || isArray(value); }, message: '"audience" must be a string or array' },
+  algorithm: { isValid: includes.bind(null, ['RS256', 'RS384', 'RS512', 'ES256', 'ES384', 'ES512', 'HS256', 'HS384', 'HS512', 'none']), message: '"algorithm" must be a valid string enum value' },
+  header: { isValid: isPlainObject, message: '"header" must be an object' },
+  encoding: { isValid: isString, message: '"encoding" must be a string' },
+  issuer: { isValid: isString, message: '"issuer" must be a string' },
+  subject: { isValid: isString, message: '"subject" must be a string' },
+  jwtid: { isValid: isString, message: '"jwtid" must be a string' },
+  noTimestamp: { isValid: isBoolean, message: '"noTimestamp" must be a boolean' },
+  keyid: { isValid: isString, message: '"keyid" must be a string' },
+};
+
+var registered_claims_schema = {
+  iat: { isValid: isNumber, message: '"iat" should be a number of seconds' },
+  exp: { isValid: isNumber, message: '"exp" should be a number of seconds' },
+  nbf: { isValid: isNumber, message: '"nbf" should be a number of seconds' }
+};
 
+function validate(schema, unknown, object) {
+  if (!isPlainObject(object)) {
+    throw new Error('Expected object');
+  }
+  Object.keys(object)
+    .forEach(function(key) {
+      var validator = schema[key];
+      if (!validator) {
+        if (!unknown) {
+          throw new Error('"' + key + '" is not allowed');
+        }
+        return;
+      }
+      if (!validator.isValid(object[key])) {
+        throw new Error(validator.message);
+      }
+    });
+}
 
 var options_to_payload = {
   'audience': 'aud',
@@ -73,12 +97,12 @@ module.exports = function (payload, secretOrPrivateKey, options, callback) {
   if (typeof payload === 'undefined') {
     return failure(new Error('payload is required'));
   } else if (isObjectPayload) {
-    var payload_validation_result = registered_claims_schema.validate(payload);
-
-    if (payload_validation_result.error) {
-      return failure(payload_validation_result.error);
+    try {
+      validate(registered_claims_schema, true, payload);
+    }
+    catch (error) {
+      return failure(error);
     }
-
     payload = xtend(payload);
   } else {
     var invalid_options = options_for_objects.filter(function (opt) {
@@ -98,10 +122,11 @@ module.exports = function (payload, secretOrPrivateKey, options, callback) {
     return failure(new Error('Bad "options.notBefore" option the payload already has an "nbf" property.'));
   }
 
-  var validation_result = sign_options_schema.validate(options);
-
-  if (validation_result.error) {
-    return failure(validation_result.error);
+  try {
+    validate(sign_options_schema, false, options);
+  }
+  catch (error) {
+    return failure(error);
   }
 
   var timestamp = payload.iat || Math.floor(Date.now() / 1000);
diff --git a/test/expires_format.tests.js b/test/expires_format.tests.js
index 42d18a5..7e542c4 100644
--- a/test/expires_format.tests.js
+++ b/test/expires_format.tests.js
@@ -33,7 +33,7 @@ describe('expires option', function() {
   it('should throw if expires is not an string or number', function () {
     expect(function () {
       jwt.sign({foo: 123}, '123', { expiresIn: { crazy : 213 } });
-    }).to.throw(/"expiresIn" must be a number/);
+    }).to.throw(/"expiresIn" should be a number of seconds or string representing a timespan/);
   });
 
   it('should throw an error if expiresIn and exp are provided', function () {
diff --git a/test/iat.tests.js b/test/iat.tests.js
index 6d2c2c0..72d7a1a 100644
--- a/test/iat.tests.js
+++ b/test/iat.tests.js
@@ -12,11 +12,4 @@ describe('iat', function () {
     expect(result.exp).to.be.closeTo(iat + expiresIn, 0.2);
   });
 
-
-  it('should throw if iat is not a number', function () {
-    expect(function () {
-      jwt.sign({foo: 123, iat: 'hello'}, '123');
-    }).to.throw(/"iat" must be a number/);
-  });
-
 });
\ No newline at end of file
diff --git a/test/schema.tests.js b/test/schema.tests.js
new file mode 100644
index 0000000..1f79994
--- /dev/null
+++ b/test/schema.tests.js
@@ -0,0 +1,136 @@
+var jwt = require('../index');
+var expect = require('chai').expect;
+var fs = require('fs');
+
+describe('schema', function() {
+
+  describe('sign options', function() {
+
+    var cert_rsa_priv = fs.readFileSync(__dirname + '/rsa-private.pem');
+    var cert_ecdsa_priv = fs.readFileSync(__dirname + '/ecdsa-private.pem');
+
+    function sign(options) {
+      var isEcdsa = options.algorithm && options.algorithm.indexOf('ES') === 0;
+      jwt.sign({foo: 123}, isEcdsa ? cert_ecdsa_priv : cert_rsa_priv, options);
+    }
+
+    it('should validate expiresIn', function () {
+      expect(function () {
+        sign({ expiresIn: '1 monkey' });
+      }).to.throw(/"expiresIn" should be a number of seconds or string representing a timespan/);
+      expect(function () {
+        sign({ expiresIn: 1.1 });
+      }).to.throw(/"expiresIn" should be a number of seconds or string representing a timespan/);
+      sign({ expiresIn: '10s' });
+      sign({ expiresIn: 10 });
+    });
+
+    it('should validate notBefore', function () {
+      expect(function () {
+        sign({ notBefore: '1 monkey' });
+      }).to.throw(/"notBefore" should be a number of seconds or string representing a timespan/);
+      expect(function () {
+        sign({ notBefore: 1.1 });
+      }).to.throw(/"notBefore" should be a number of seconds or string representing a timespan/);
+      sign({ notBefore: '10s' });
+      sign({ notBefore: 10 });
+    });
+
+    it('should validate audience', function () {
+      expect(function () {
+        sign({ audience: 10 });
+      }).to.throw(/"audience" must be a string or array/);
+      sign({ audience: 'urn:foo' });
+      sign({ audience: ['urn:foo'] });
+    });
+
+    it('should validate algorithm', function () {
+      expect(function () {
+        sign({ algorithm: 'foo' });
+      }).to.throw(/"algorithm" must be a valid string enum value/);
+      sign({algorithm: 'RS256'});
+      sign({algorithm: 'RS384'});
+      sign({algorithm: 'RS512'});
+      sign({algorithm: 'ES256'});
+      sign({algorithm: 'ES384'});
+      sign({algorithm: 'ES512'});
+      sign({algorithm: 'HS256'});
+      sign({algorithm: 'HS384'});
+      sign({algorithm: 'HS512'});
+      sign({algorithm: 'none'});
+    });
+
+    it('should validate header', function () {
+      expect(function () {
+        sign({ header: 'foo' });
+      }).to.throw(/"header" must be an object/);
+      sign({header: {}});
+    });
+
+    it('should validate encoding', function () {
+      expect(function () {
+        sign({ encoding: 10 });
+      }).to.throw(/"encoding" must be a string/);
+      sign({encoding: 'utf8'});
+    });
+
+    it('should validate issuer', function () {
+      expect(function () {
+        sign({ issuer: 10 });
+      }).to.throw(/"issuer" must be a string/);
+      sign({issuer: 'foo'});
+    });
+
+    it('should validate subject', function () {
+      expect(function () {
+        sign({ subject: 10 });
+      }).to.throw(/"subject" must be a string/);
+      sign({subject: 'foo'});
+    });
+
+    it('should validate noTimestamp', function () {
+      expect(function () {
+        sign({ noTimestamp: 10 });
+      }).to.throw(/"noTimestamp" must be a boolean/);
+      sign({noTimestamp: true});
+    });
+
+    it('should validate keyid', function () {
+      expect(function () {
+        sign({ keyid: 10 });
+      }).to.throw(/"keyid" must be a string/);
+      sign({keyid: 'foo'});
+    });
+
+  });
+
+  describe('sign payload registered claims', function() {
+
+    function sign(payload) {
+      jwt.sign(payload, 'foo123');
+    }
+
+    it('should validate iat', function () {
+      expect(function () {
+        sign({ iat: '1 monkey' });
+      }).to.throw(/"iat" should be a number of seconds/);
+      sign({ iat: 10.1 });
+    });
+
+    it('should validate exp', function () {
+      expect(function () {
+        sign({ exp: '1 monkey' });
+      }).to.throw(/"exp" should be a number of seconds/);
+      sign({ exp: 10.1 });
+    });
+
+    it('should validate nbf', function () {
+      expect(function () {
+        sign({ nbf: '1 monkey' });
+      }).to.throw(/"nbf" should be a number of seconds/);
+      sign({ nbf: 10.1 });
+    });
+
+  });
+
+});
\ No newline at end of file