diff --git a/gulpfile.js b/gulpfile.js
index c2c86f0..f60156d 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -17,7 +17,9 @@ var REQUIRE_PATTERN = /((?:var |,)[^=]+=\s*require\([^\)]+\);?\n?)/g;
 var EXPORT_PATTERN = /((?:module\.)?exports\s*=\s*[^,;]+;?\n?)/g;
 
 var files = [
+    './src/maxSafeInteger.js',
     './src/isFinite.js',
+    './src/isSafeNumber.js',
     './src/makeOrdinal.js',
     './src/toOrdinal.js',
     './src/toWords.js',
diff --git a/spec/isSafeNumberSpec.js b/spec/isSafeNumberSpec.js
new file mode 100644
index 0000000..cd15463
--- /dev/null
+++ b/spec/isSafeNumberSpec.js
@@ -0,0 +1,30 @@
+'use strict';
+
+var MAX_SAFE_INTEGER = require('../src/maxSafeInteger');
+var isSafeNumber = require('../src/isSafeNumber');
+
+describe('isSafeNumber', function() {
+    it('should return true if input is a number between -MAX_SAFE_INTEGER and MAX_SAFE_INTEGER (including)', function() {
+        expect(isSafeNumber(-MAX_SAFE_INTEGER)).toBe(true);
+        expect(isSafeNumber(-1)).toBe(true);
+        expect(isSafeNumber(0)).toBe(true);
+        expect(isSafeNumber(1)).toBe(true);
+        expect(isSafeNumber(MAX_SAFE_INTEGER)).toBe(true);
+    });
+    it('should return false if input is too large or too small', function() {
+        var unsafe = MAX_SAFE_INTEGER + 100;
+
+        expect(isSafeNumber(unsafe)).toBe(false);
+        expect(isSafeNumber(-unsafe)).toBe(false);
+    });
+    it('should return false if input is not a number', function() {
+        expect(isSafeNumber()).toBe(false);
+        expect(isSafeNumber(null)).toBe(false);
+        expect(isSafeNumber([])).toBe(false);
+        expect(isSafeNumber({})).toBe(false);
+        expect(isSafeNumber('')).toBe(false);
+        expect(isSafeNumber('x')).toBe(false);
+        expect(isSafeNumber(function() {})).toBe(false);
+        expect(isSafeNumber(NaN)).toBe(false);
+    });
+});
diff --git a/spec/toOrdinalSpec.js b/spec/toOrdinalSpec.js
index af88224..124c4a8 100644
--- a/spec/toOrdinalSpec.js
+++ b/spec/toOrdinalSpec.js
@@ -1,6 +1,7 @@
 'use strict';
 
 var toOrdinal = typeof require !== 'undefined' ? require('../src/toOrdinal') : window.numberToWords.toOrdinal;
+var MAX_SAFE_INTEGER = 9007199254740991;
 
 describe('toOrdinal', function () {
     var tests = [
@@ -36,4 +37,16 @@ describe('toOrdinal', function () {
     }
 
     tests.forEach(addTest);
+
+    it('should throw a RangeError if input is greater or lesser than MAX_SAFE_INTEGER', function() {
+        var unsafe = MAX_SAFE_INTEGER + 100;
+
+        expect(function() {
+            toOrdinal(unsafe);
+        }).toThrowError(/Input is not a safe number/);
+
+        expect(function() {
+            toOrdinal(-unsafe);
+        }).toThrowError(/Input is not a safe number/);
+    });
 });
diff --git a/spec/toWordsSpec.js b/spec/toWordsSpec.js
index 0fd0927..ee9e1f4 100644
--- a/spec/toWordsSpec.js
+++ b/spec/toWordsSpec.js
@@ -1,5 +1,6 @@
 'use strict';
 
+var MAX_SAFE_INTEGER = 9007199254740991;
 var toWords = typeof require !== 'undefined' ? require('../src/toWords') : window.numberToWords.toWords;
 
 describe('toWords', function () {
@@ -88,8 +89,8 @@ describe('toWords', function () {
             expect: 'five quadrillion, five hundred fifty-five trillion, five hundred fifty-five billion, five hundred fifty-five million, five hundred fifty-five thousand, five hundred fifty-five'
         },
         {
-            input: 9007199254740992,
-            expect: 'nine quadrillion, seven trillion, one hundred ninety-nine billion, two hundred fifty-four million, seven hundred forty thousand, nine hundred ninety-two'
+            input: MAX_SAFE_INTEGER,
+            expect: 'nine quadrillion, seven trillion, one hundred ninety-nine billion, two hundred fifty-four million, seven hundred forty thousand, nine hundred ninety-one'
         }
     ];
 
@@ -111,6 +112,18 @@ describe('toWords', function () {
         expect(toWords(30, true)).toEqual('thirtieth');
         expect(toWords(123, true)).toEqual('one hundred twenty-third');
     });
+    
+    it('should throw a RangeError if input is greater or lesser than MAX_SAFE_INTEGER', function() {
+        var unsafe = MAX_SAFE_INTEGER + 100;
+
+        expect(function() {
+            toWords(unsafe);
+        }).toThrowError(/Input is not a safe number/);
+
+        expect(function() {
+            toWords(-unsafe);
+        }).toThrowError(/Input is not a safe number/);
+    });
 });
 
 function formatNumber(number) {
diff --git a/src/isSafeNumber.js b/src/isSafeNumber.js
new file mode 100644
index 0000000..ae43920
--- /dev/null
+++ b/src/isSafeNumber.js
@@ -0,0 +1,9 @@
+'use strict';
+
+var MAX_SAFE_INTEGER = require('./maxSafeInteger');
+
+function isSafeNumber(value) {
+    return typeof value === 'number' && Math.abs(value) <= MAX_SAFE_INTEGER;
+}
+
+module.exports = isSafeNumber;
diff --git a/src/maxSafeInteger.js b/src/maxSafeInteger.js
new file mode 100644
index 0000000..ff6d6f6
--- /dev/null
+++ b/src/maxSafeInteger.js
@@ -0,0 +1,5 @@
+'use strict';
+
+var MAX_SAFE_INTEGER = 9007199254740991;
+
+module.exports = MAX_SAFE_INTEGER;
diff --git a/src/toOrdinal.js b/src/toOrdinal.js
index 666d88d..80528b2 100644
--- a/src/toOrdinal.js
+++ b/src/toOrdinal.js
@@ -1,6 +1,7 @@
 'use strict';
 
 var isFinite = require('./isFinite');
+var isSafeNumber = require('./isSafeNumber');
 
 /**
  * Converts an integer into a string with an ordinal postfix.
@@ -11,7 +12,17 @@ var isFinite = require('./isFinite');
  */
 function toOrdinal(number) {
     var num = parseInt(number, 10);
-    if (!isFinite(num)) throw new TypeError('Not a finite number: ' + number + ' (' + typeof number + ')');
+
+    if (!isFinite(num)) {
+        throw new TypeError(
+            'Not a finite number: ' + number + ' (' + typeof number + ')'
+        );
+    }
+    if (!isSafeNumber(num)) {
+        throw new RangeError(
+            'Input is not a safe number, it’s either too large or too small.'
+        );
+    }
     var str = String(num);
     var lastTwoDigits = Math.abs(num % 100);
     var betweenElevenAndThirteen = lastTwoDigits >= 11 && lastTwoDigits <= 13;
diff --git a/src/toWords.js b/src/toWords.js
index ee1b204..4325613 100644
--- a/src/toWords.js
+++ b/src/toWords.js
@@ -2,6 +2,7 @@
 
 var makeOrdinal = require('./makeOrdinal');
 var isFinite = require('./isFinite');
+var isSafeNumber = require('./isSafeNumber');
 
 var TEN = 10;
 var ONE_HUNDRED = 100;
@@ -32,7 +33,17 @@ var TENTHS_LESS_THAN_HUNDRED = [
 function toWords(number, asOrdinal) {
     var words;
     var num = parseInt(number, 10);
-    if (!isFinite(num)) throw new TypeError('Not a finite number: ' + number + ' (' + typeof number + ')');
+
+    if (!isFinite(num)) {
+        throw new TypeError(
+            'Not a finite number: ' + number + ' (' + typeof number + ')'
+        );
+    }
+    if (!isSafeNumber(num)) {
+        throw new RangeError(
+            'Input is not a safe number, it’s either too large or too small.'
+        );
+    }
     words = generateWords(num);
     return asOrdinal ? makeOrdinal(words) : words;
 }