diff --git a/src/wp-includes/class-wp-widget.php b/src/wp-includes/class-wp-widget.php
index 114328d499..0681d3715c 100644
--- a/src/wp-includes/class-wp-widget.php
+++ b/src/wp-includes/class-wp-widget.php
@@ -177,11 +177,17 @@ class WP_Widget {
 	 *
 	 * This function should be used in form() methods to create name attributes for fields to be saved by update()
 	 *
+	 * @since 4.4.0 Array format field names are now accepted.
+	 *
 	 * @param string $field_name Field name
 	 * @return string Name attribute for $field_name
 	 */
 	public function get_field_name($field_name) {
-		return 'widget-' . $this->id_base . '[' . $this->number . '][' . $field_name . ']';
+		if ( false === $pos = strpos( $field_name, '[' ) ) {
+			return 'widget-' . $this->id_base . '[' . $this->number . '][' . $field_name . ']';
+		} else {
+			return 'widget-' . $this->id_base . '[' . $this->number . '][' . substr_replace( $field_name, '][', $pos, strlen( '[' ) );
+		}
 	}
 
 	/**
@@ -190,6 +196,8 @@ class WP_Widget {
 	 * This function should be used in form() methods to create id attributes
 	 * for fields to be saved by {@see WP_Widget::update()}.
 	 *
+	 * @since 4.4.0 Array format field IDs are now accepted.
+	 *
 	 * @since 2.8.0
 	 * @access public
 	 *
@@ -197,7 +205,7 @@ class WP_Widget {
 	 * @return string ID attribute for `$field_name`.
 	 */
 	public function get_field_id( $field_name ) {
-		return 'widget-' . $this->id_base . '-' . $this->number . '-' . $field_name;
+		return 'widget-' . $this->id_base . '-' . $this->number . '-' . trim( str_replace( array( '[]', '[', ']' ), array( '', '-', '' ), $field_name ), '-' );
 	}
 
 	/**
diff --git a/tests/phpunit/tests/widgets.php b/tests/phpunit/tests/widgets.php
index 0086518b77..3aa6e73dd3 100644
--- a/tests/phpunit/tests/widgets.php
+++ b/tests/phpunit/tests/widgets.php
@@ -157,20 +157,104 @@ class Tests_Widgets extends WP_UnitTestCase {
 
 	/**
 	 * @see WP_Widget::get_field_name()
+	 * @dataProvider data_wp_widget_get_field_name
+	 *
 	 */
-	function test_wp_widget_get_field_name() {
+	function test_wp_widget_get_field_name( $expected, $value_to_test ) {
 		$widget = new WP_Widget( 'foo', 'Foo' );
 		$widget->_set( 2 );
-		$this->assertEquals( 'widget-foo[2][title]', $widget->get_field_name( 'title' ) );
+		$this->assertEquals( $expected, $widget->get_field_name( $value_to_test ) );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * Passes the expected field name and the value to test.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @return array {
+	 *     @type array {
+	 *         @type string $expected      The expected field id to be returned.
+	 *         @type string $value_to_test The value being passed to the get_field_name method.
+	 *     }
+	 * }
+	 */
+	function data_wp_widget_get_field_name( ) {
+
+		return array(
+			array(
+				'widget-foo[2][title]',
+				'title',
+			),
+			array(
+				'widget-foo[2][posttypes][]',
+				'posttypes[]',
+			),
+			array(
+				'widget-foo[2][posttypes][4]',
+				'posttypes[4]',
+			),
+			array(
+				'widget-foo[2][posttypes][4][]',
+				'posttypes[4][]',
+			),
+			array(
+				'widget-foo[2][posttypes][4][][6]',
+				'posttypes[4][][6]',
+			),
+		);
 	}
 
 	/**
 	 * @see WP_Widget::get_field_id()
+	 * @dataProvider data_wp_widget_get_field_id
+	 *
 	 */
-	function test_wp_widget_get_field_id() {
+	function test_wp_widget_get_field_id( $expected, $value_to_test ) {
 		$widget = new WP_Widget( 'foo', 'Foo' );
 		$widget->_set( 2 );
-		$this->assertEquals( 'widget-foo-2-title', $widget->get_field_id( 'title' ) );
+		$this->assertEquals( $expected, $widget->get_field_id( $value_to_test ) );
+	}
+
+
+	/**
+	 * Data provider.
+	 *
+	 * Passes the expected field id and the value to be used in the tests.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @return array {
+	 *     @type array {
+	 *         @type string $expected      The expected field id to be returned.
+	 *         @type string $value_to_test The value being passed to the get_field_id method.
+	 *     }
+	 * }
+	 */
+	function data_wp_widget_get_field_id() {
+		return array(
+			array(
+				'widget-foo-2-title',
+				'title',
+			),
+			array(
+				'widget-foo-2-posttypes',
+				'posttypes[]',
+			),
+			array(
+				'widget-foo-2-posttypes-4',
+				'posttypes[4]',
+			),
+			array(
+				'widget-foo-2-posttypes-4',
+				'posttypes[4][]',
+			),
+			array(
+				'widget-foo-2-posttypes-4-6',
+				'posttypes[4][][6]',
+			),
+		);
 	}
 
 	/**