diff --git a/lib/command-line-args.js b/lib/command-line-args.js
index 7581abf..33a397c 100644
--- a/lib/command-line-args.js
+++ b/lib/command-line-args.js
@@ -34,8 +34,9 @@ module.exports = commandLineArgs
  * ])
  * ```
  */
-function commandLineArgs (definitions, argv) {
-  definitions = new Definitions(definitions)
+function commandLineArgs (optionDefinitions, argv) {
+  const definitions = new Definitions()
+  definitions.load(optionDefinitions)
   argv = new Argv(argv)
   argv.expandOptionEqualsNotation()
   argv.expandGetoptNotation()
diff --git a/lib/definitions.js b/lib/definitions.js
index 26b4b51..11a2f8a 100644
--- a/lib/definitions.js
+++ b/lib/definitions.js
@@ -12,10 +12,9 @@ const t = require('typical')
 /**
  * @alias module:definitions
  */
-class Definitions {
-  constructor (definitions) {
-    this.list = []
-    arrayify(definitions).forEach(def => this.list.push(new Definition(def)))
+class Definitions extends Array {
+  load (definitions) {
+    arrayify(definitions).forEach(def => this.push(new Definition(def)))
     this.validate()
   }
 
@@ -24,7 +23,7 @@ class Definitions {
    * @returns {string}
    */
   validate (argv) {
-    const someHaveNoName = this.list.some(def => !def.name)
+    const someHaveNoName = this.some(def => !def.name)
     if (someHaveNoName) {
       halt(
         'NAME_MISSING',
@@ -32,7 +31,7 @@ class Definitions {
       )
     }
 
-    const someDontHaveFunctionType = this.list.some(def => def.type && typeof def.type !== 'function')
+    const someDontHaveFunctionType = this.some(def => def.type && typeof def.type !== 'function')
     if (someDontHaveFunctionType) {
       halt(
         'INVALID_TYPE',
@@ -42,7 +41,7 @@ class Definitions {
 
     let invalidOption
 
-    const numericAlias = this.list.some(def => {
+    const numericAlias = this.some(def => {
       invalidOption = def
       return t.isDefined(def.alias) && t.isNumber(def.alias)
     })
@@ -53,7 +52,7 @@ class Definitions {
       )
     }
 
-    const multiCharacterAlias = this.list.some(def => {
+    const multiCharacterAlias = this.some(def => {
       invalidOption = def
       return t.isDefined(def.alias) && def.alias.length !== 1
     })
@@ -64,7 +63,7 @@ class Definitions {
       )
     }
 
-    const hypenAlias = this.list.some(def => {
+    const hypenAlias = this.some(def => {
       invalidOption = def
       return def.alias === '-'
     })
@@ -75,7 +74,7 @@ class Definitions {
       )
     }
 
-    const duplicateName = hasDuplicates(this.list.map(def => def.name))
+    const duplicateName = hasDuplicates(this.map(def => def.name))
     if (duplicateName) {
       halt(
         'DUPLICATE_NAME',
@@ -83,7 +82,7 @@ class Definitions {
       )
     }
 
-    const duplicateAlias = hasDuplicates(this.list.map(def => def.alias))
+    const duplicateAlias = hasDuplicates(this.map(def => def.alias))
     if (duplicateAlias) {
       halt(
         'DUPLICATE_ALIAS',
@@ -91,7 +90,7 @@ class Definitions {
       )
     }
 
-    const duplicateDefaultOption = hasDuplicates(this.list.map(def => def.defaultOption))
+    const duplicateDefaultOption = hasDuplicates(this.map(def => def.defaultOption))
     if (duplicateDefaultOption) {
       halt(
         'DUPLICATE_DEFAULT_OPTION',
@@ -106,8 +105,10 @@ class Definitions {
    */
   createOutput () {
     const output = {}
-    this.list.forEach(def => {
-      if (t.isDefined(def.defaultValue)) output[def.name] = def.defaultValue
+    this.forEach(def => {
+      if (t.isDefined(def.defaultValue)) {
+        output[def.name] = def.multiple ? arrayify(def.defaultValue) : def.defaultValue
+      }
       if (Array.isArray(output[def.name])) {
         output[def.name]._initial = true
       }
@@ -121,23 +122,23 @@ class Definitions {
    */
   get (arg) {
     return option.short.test(arg)
-      ? this.list.find(def => def.alias === option.short.name(arg))
-      : this.list.find(def => def.name === option.long.name(arg))
+      ? this.find(def => def.alias === option.short.name(arg))
+      : this.find(def => def.name === option.long.name(arg))
   }
 
   getDefault () {
-    return this.list.find(def => def.defaultOption === true)
+    return this.find(def => def.defaultOption === true)
   }
 
   isGrouped () {
-    return this.list.some(def => def.group)
+    return this.some(def => def.group)
   }
 
   whereGrouped () {
-    return this.list.filter(containsValidGroup)
+    return this.filter(containsValidGroup)
   }
   whereNotGrouped () {
-    return this.list.filter(def => !containsValidGroup(def))
+    return this.filter(def => !containsValidGroup(def))
   }
 
 }
diff --git a/test/class-argv.js b/test/class-argv.js
index 432c200..06614d2 100644
--- a/test/class-argv.js
+++ b/test/class-argv.js
@@ -31,7 +31,8 @@ runner.test('.expandGetoptNotation() with values', function () {
 })
 
 runner.test('.validate()', function () {
-  const definitions = new Definitions([
+  const definitions = new Definitions()
+  definitions.load([
     { name: 'one', type: Number }
   ])
 
diff --git a/test/class-definitions.js b/test/class-definitions.js
index 785bd64..1a43994 100644
--- a/test/class-definitions.js
+++ b/test/class-definitions.js
@@ -6,17 +6,20 @@ const Definitions = require('../lib/definitions')
 const runner = new TestRunner()
 
 runner.test('.createOutput()', function () {
-  const definitions = new Definitions([ { name: 'one', defaultValue: 'eins' } ])
+  const definitions = new Definitions()
+  definitions.load([ { name: 'one', defaultValue: 'eins' } ])
   a.deepStrictEqual(definitions.createOutput(), { one: 'eins' })
 })
 
 runner.test('.get()', function () {
-  const definitions = new Definitions([ { name: 'one', defaultValue: 'eins' } ])
+  const definitions = new Definitions()
+  definitions.load([ { name: 'one', defaultValue: 'eins' } ])
   a.strictEqual(definitions.get('--one').name, 'one')
 })
 
 runner.test('.validate()', function () {
   a.throws(function () {
-    const definitions = new Definitions([ { name: 'one' }, { name: 'one' } ]) // eslint-disable-line no-unused-vars
+    const definitions = new Definitions()
+    definitions.load([ { name: 'one' }, { name: 'one' } ])
   })
 })
diff --git a/test/default-value.js b/test/default-value.js
index 3c1a1ef..ac49000 100644
--- a/test/default-value.js
+++ b/test/default-value.js
@@ -48,3 +48,18 @@ runner.test('default value: falsy default values', function () {
     two: false
   })
 })
+
+runner.test('default value: is arrayifed if multiple set', function () {
+  const defs = [
+    { name: 'one', defaultValue: 0, multiple: true }
+  ]
+
+  let argv = []
+  a.deepStrictEqual(cliArgs(defs, argv), {
+    one: [ 0 ]
+  })
+  argv = [ '--one', '2' ]
+  a.deepStrictEqual(cliArgs(defs, argv), {
+    one: [ '2' ]
+  })
+})