diff --git a/src/wp-includes/widgets/class-wp-widget-custom-html.php b/src/wp-includes/widgets/class-wp-widget-custom-html.php
index 5de618285f..7447415185 100644
--- a/src/wp-includes/widgets/class-wp-widget-custom-html.php
+++ b/src/wp-includes/widgets/class-wp-widget-custom-html.php
@@ -79,7 +79,9 @@ class WP_Widget_Custom_HTML extends WP_Widget {
 		if ( ! empty( $title ) ) {
 			echo $args['before_title'] . $title . $args['after_title'];
 		}
+		echo '<div class="textwidget custom-html-widget">'; // The textwidget class is for theme styling compatibility.
 		echo $content;
+		echo '</div>';
 		echo $args['after_widget'];
 	}
 
diff --git a/tests/phpunit/tests/widgets/custom-html-widget.php b/tests/phpunit/tests/widgets/custom-html-widget.php
index c7c2e91bf8..a9fe7c33cb 100644
--- a/tests/phpunit/tests/widgets/custom-html-widget.php
+++ b/tests/phpunit/tests/widgets/custom-html-widget.php
@@ -70,6 +70,7 @@ class Test_WP_Widget_Custom_HTML extends WP_UnitTestCase {
 		$this->assertNotEmpty( $this->widget_custom_html_content_args );
 		$this->assertNotEmpty( $this->widget_text_args );
 		$this->assertContains( '[filter:widget_text][filter:widget_custom_html_content]', $output );
+		$this->assertContains( '<div class="textwidget custom-html-widget">', $output );
 		$this->assertNotContains( '<p>', $output );
 		$this->assertNotContains( '<br>', $output );
 		$this->assertNotContains( '</u>', $output );