diff --git a/es5/definition.js b/es5/definition.js
index ae28cd0..a083233 100644
--- a/es5/definition.js
+++ b/es5/definition.js
@@ -4,6 +4,8 @@ var _createClass = function () { function defineProperties(target, props) { for
 
 function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
 
+var t = require('typical');
+
 var OptionDefinition = function () {
   function OptionDefinition(definition) {
     _classCallCheck(this, OptionDefinition);
@@ -41,19 +43,15 @@ var OptionDefinition = function () {
   }, {
     key: 'isBoolean',
     value: function isBoolean() {
-      if (!this.type) {
+      if (this.type) {
+        return this.type === Boolean || t.isFunction(this.type) && this.type.name === 'Boolean';
+      } else {
         return false;
-      } else { // Fall back to ES5 Method
-        var result = /^function\s+([\w\$]+)\s*\(/.exec( this.type.toString() );
-        if (result && result.length>=2 && result[1] == "Boolean") {
-            return true;
-        }
       }
-      return false;
     }
   }]);
 
   return OptionDefinition;
 }();
 
-module.exports = OptionDefinition;
+module.exports = OptionDefinition;
\ No newline at end of file
diff --git a/lib/definition.js b/lib/definition.js
index a53953c..c6492ec 100644
--- a/lib/definition.js
+++ b/lib/definition.js
@@ -1,4 +1,6 @@
 'use strict'
+const t = require('typical')
+
 /**
  * @module definition
  */
@@ -236,17 +238,11 @@ class OptionDefinition {
   }
 
   isBoolean () {
-    if (!this.type) {
-        return false;
-    } else if (this.type.name == "Boolean") { // First try ES6 Method
-        return true;
-    } else { // Fall back to ES5 Method
-        var result = /^function\s+([\w\$]+)\s*\(/.exec( this.type.toString() );
-        if (result && result.length>=2 && result[1] == "Boolean") {
-            return true;
-        }
+    if (this.type) {
+      return this.type === Boolean || (t.isFunction(this.type) && this.type.name === 'Boolean')
+    } else {
+      return false
     }
-    return false;
   }
 }
 
diff --git a/package.json b/package.json
index 7cdcbe6..aa709ce 100644
--- a/package.json
+++ b/package.json
@@ -31,7 +31,7 @@
     "core-assert": "~0.2.0",
     "coveralls": "^2.11.12",
     "jsdoc-to-markdown": "^1.3.6",
-    "test-runner": "~0.1.4",
+    "test-runner": "~0.1.6",
     "test-value": "^2.0.0"
   },
   "dependencies": {
diff --git a/test/default-option.js b/test/default-option.js
index 2be4b2d..d82cbb5 100644
--- a/test/default-option.js
+++ b/test/default-option.js
@@ -32,7 +32,6 @@ test('defaultOption: after a boolean', function () {
     cliArgs(definitions, [ '--one', 'sfsgf' ]),
     { one: true, two: 'sfsgf' }
   )
-
 })
 
 test('defaultOption: multiple defaultOption values between other arg/value pairs', function () {
@@ -71,5 +70,4 @@ test('defaultOption: floating args present but no defaultOption', function () {
     cliArgs(definitions, [ 'aaa', '--one', 'aaa', 'aaa' ]),
     { one: true }
   )
-
 })
diff --git a/test/exceptions.js b/test/exceptions.js
index 9887155..c67d63a 100644
--- a/test/exceptions.js
+++ b/test/exceptions.js
@@ -29,7 +29,6 @@ test('err-invalid-definition: throws if dev set a numeric alias', function () {
   } catch (err) {
     a.strictEqual(err.name, 'INVALID_ALIAS')
   }
-
 })
 
 test('err-invalid-definition: throws if dev set an alias of "-"', function () {
@@ -44,7 +43,6 @@ test('err-invalid-definition: throws if dev set an alias of "-"', function () {
   } catch (err) {
     a.strictEqual(err.name, 'INVALID_ALIAS')
   }
-
 })
 
 test('err-invalid-definition: multi-character alias', function () {
@@ -59,7 +57,6 @@ test('err-invalid-definition: multi-character alias', function () {
   } catch (err) {
     a.strictEqual(err.name, 'INVALID_ALIAS')
   }
-
 })
 
 test('err-invalid-definition: invalid type values', function () {
@@ -88,7 +85,6 @@ test('err-invalid-definition: invalid type values', function () {
   a.doesNotThrow(function () {
     cliArgs([ { name: 'one', type: function () {} } ], argv)
   }, /invalid/i)
-
 })
 
 test('err-invalid-definition: value without option definition', function () {
@@ -128,7 +124,6 @@ test('err-invalid-definition: value without option definition', function () {
   } catch (err) {
     a.strictEqual(err.name, 'UNKNOWN_OPTION', 'getOpts')
   }
-
 })
 
 test('err-invalid-definition: duplicate name', function () {
@@ -144,7 +139,6 @@ test('err-invalid-definition: duplicate name', function () {
   } catch (err) {
     a.strictEqual(err.name, 'DUPLICATE_NAME')
   }
-
 })
 
 test('err-invalid-definition: duplicate alias', function () {
@@ -160,7 +154,6 @@ test('err-invalid-definition: duplicate alias', function () {
   } catch (err) {
     a.strictEqual(err.name, 'DUPLICATE_ALIAS')
   }
-
 })
 
 test('err-invalid-definition: multiple defaultOption', function () {
@@ -176,5 +169,4 @@ test('err-invalid-definition: multiple defaultOption', function () {
   } catch (err) {
     a.strictEqual(err.name, 'DUPLICATE_DEFAULT_OPTION')
   }
-
 })
diff --git a/test/type-boolean.js b/test/type-boolean.js
index 2a9f2ee..8b837ee 100644
--- a/test/type-boolean.js
+++ b/test/type-boolean.js
@@ -3,11 +3,11 @@ var test = require('test-runner')
 var cliArgs = require('../')
 var a = require('core-assert')
 
-var optionDefinitions = [
-  { name: 'one', type: Boolean }
-]
-
 test('type-boolean: different values', function () {
+  var optionDefinitions = [
+    { name: 'one', type: Boolean }
+  ]
+
   a.deepStrictEqual(
     cliArgs(optionDefinitions, [ '--one' ]),
     { one: true }
@@ -25,3 +25,33 @@ test('type-boolean: different values', function () {
     { one: true }
   )
 })
+
+var origBoolean = Boolean
+
+/* test in contexts which override the standard global Boolean constructor */
+test('type-boolean: global Boolean overridden', function () {
+  function Boolean () {
+    return origBoolean.apply(origBoolean, arguments)
+  }
+
+  var optionDefinitions = [
+    { name: 'one', type: Boolean }
+  ]
+
+  a.deepStrictEqual(
+    cliArgs(optionDefinitions, [ '--one', 'true' ]),
+    { one: true }
+  )
+  a.deepStrictEqual(
+    cliArgs(optionDefinitions, [ '--one', 'false' ]),
+    { one: true }
+  )
+  a.deepStrictEqual(
+    cliArgs(optionDefinitions, [ '--one', 'sfsgf' ]),
+    { one: true }
+  )
+  a.deepStrictEqual(
+    cliArgs(optionDefinitions, [ '--one' ]),
+    { one: true }
+  )
+})
diff --git a/test/type-other.js b/test/type-other.js
index 888e4cf..0f4ad27 100644
--- a/test/type-other.js
+++ b/test/type-other.js
@@ -3,13 +3,13 @@ var test = require('test-runner')
 var cliArgs = require('../')
 var a = require('core-assert')
 
-var optionDefinitions = [
-  { name: 'file', type: function (file) {
-    return file
-  }}
-]
-
 test('type-other: different values', function () {
+  var optionDefinitions = [
+    { name: 'file', type: function (file) {
+      return file
+    }}
+  ]
+
   a.deepStrictEqual(
     cliArgs(optionDefinitions, [ '--file', 'one.js' ]),
     { file: 'one.js' }
@@ -19,3 +19,14 @@ test('type-other: different values', function () {
     { file: null }
   )
 })
+
+test('type-other: broken custom type function', function () {
+  var optionDefinitions = [
+    { name: 'file', type: function (file) {
+      lasdfjsfakn
+    }}
+  ]
+  a.throws(function () {
+    cliArgs(optionDefinitions, [ '--file', 'one.js' ])
+  })
+})
diff --git a/test/type-string.js b/test/type-string.js
index ff6e6a3..426f193 100644
--- a/test/type-string.js
+++ b/test/type-string.js
@@ -28,5 +28,4 @@ test.skip('type-string: pass a value resembling an option', function () {
     cliArgs(optionDefinitions, [ '--one', '--yeah' ]),
     { one: '--yeah' }
   )
-  t.end()
 })