diff --git a/includes/widgets/class-amp-widget-archives.php b/includes/widgets/class-amp-widget-archives.php
index 2c232ffc0fe..69a9649ac7d 100644
--- a/includes/widgets/class-amp-widget-archives.php
+++ b/includes/widgets/class-amp-widget-archives.php
@@ -15,17 +15,80 @@ class AMP_Widget_Archives extends WP_Widget_Archives {
 	/**
 	 * Echoes the markup of the widget.
 	 *
-	 * @todo filter $output, to strip the onchange attribute
-	 * @see https://github.com/Automattic/amp-wp/issues/864
+	 * Mainly copied from WP_Widget_Archives::widget()
+	 * Changes include:
+	 * An id for the <form>.
+	 * More escaping.
+	 * The dropdown is now filtered with 'wp_dropdown_cats.'
+	 * This enables adding an 'on' attribute, with the id of the form.
+	 * So changing the dropdown value will redirect to the category page, with valid AMP.
+	 *
 	 * @param array $args Widget display data.
 	 * @param array $instance Data for widget.
 	 * @return void.
 	 */
 	public function widget( $args, $instance ) {
-		ob_start();
-		parent::widget( $args, $instance );
-		$output = ob_get_clean();
-		echo AMP_Theme_Support::filter_the_content( $output ); // WPCS: XSS ok.
+		$c = ! empty( $instance['count'] ) ? '1' : '0';
+		$d = ! empty( $instance['dropdown'] ) ? '1' : '0';
+
+		/** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
+		$title = apply_filters( 'widget_title', empty( $instance['title'] ) ? __( 'Archives', 'default' ) : $instance['title'], $instance, $this->id_base );
+		echo wp_kses_post( $args['before_widget'] );
+		if ( $title ) :
+			echo wp_kses_post( $args['before_title'] . $title . $args['after_title'] );
+		endif;
+
+		if ( $d ) :
+			$dropdown_id = "{$this->id_base}-dropdown-{$this->number}";
+			?>
+			<form action="<?php echo esc_url( home_url() ); ?>" method="get" id="widget-archives-dropdown-<?php echo esc_attr( $this->number ); ?>">
+				<label class="screen-reader-text" for="<?php echo esc_attr( $dropdown_id ); ?>"><?php echo esc_html( $title ); ?></label>
+				<select id="<?php echo esc_attr( $dropdown_id ); ?>" name="archive-dropdown" on="change:widget-archives-dropdown-<?php echo esc_attr( $this->number ); ?>.submit">
+					<?php
+
+					/** This filter is documented in wp-includes/widgets/class-wp-widget-archives.php */
+					$dropdown_args = apply_filters( 'widget_archives_dropdown_args', array(
+						'type'            => 'monthly',
+						'format'          => 'option',
+						'show_post_count' => $c,
+					) );
+
+					switch ( $dropdown_args['type'] ) {
+						case 'yearly':
+							$label = __( 'Select Year', 'default' );
+							break;
+						case 'monthly':
+							$label = __( 'Select Month', 'default' );
+							break;
+						case 'daily':
+							$label = __( 'Select Day', 'default' );
+							break;
+						case 'weekly':
+							$label = __( 'Select Week', 'default' );
+							break;
+						default:
+							$label = __( 'Select Post', 'default' );
+							break;
+					}
+					?>
+					<option value=""><?php echo esc_attr( $label ); ?></option>
+					<?php wp_get_archives( $dropdown_args ); ?>
+				</select>
+			</form>
+		<?php else : ?>
+			<ul>
+				<?php
+
+				/** This filter is documented in wp-includes/widgets/class-wp-widget-archives.php */
+				wp_get_archives( apply_filters( 'widget_archives_args', array(
+					'type'            => 'monthly',
+					'show_post_count' => $c,
+				) ) );
+				?>
+			</ul>
+		<?php
+		endif;
+		echo wp_kses_post( $args['after_widget'] );
 	}
 
 }
diff --git a/includes/widgets/class-amp-widget-categories.php b/includes/widgets/class-amp-widget-categories.php
index 00c3889acf1..c9d17e17ccd 100644
--- a/includes/widgets/class-amp-widget-categories.php
+++ b/includes/widgets/class-amp-widget-categories.php
@@ -71,15 +71,8 @@ public function widget( $args, $instance ) {
 			<ul>
 			<?php
 			$cat_args['title_li'] = '';
-			/**
-			 * Filters the arguments for the Categories widget.
-			 *
-			 * @since 2.8.0
-			 * @since 4.9.0 Added the `$instance` parameter.
-			 *
-			 * @param array $cat_args An array of Categories widget options.
-			 * @param array $instance Array of settings for the current widget.
-			 */
+
+			/** This filter is documented in wp-includes/widgets/class-wp-widget-categories.php */
 			wp_list_categories( apply_filters( 'widget_categories_args', $cat_args, $instance ) );
 			?>
 			</ul>
diff --git a/tests/test-class-amp-widget-media-audio.php b/tests/test-class-amp-widget-media-audio.php
index 758b58f9c0c..c66aee65a05 100644
--- a/tests/test-class-amp-widget-media-audio.php
+++ b/tests/test-class-amp-widget-media-audio.php
@@ -50,7 +50,7 @@ public function test_construct() {
 	 */
 	public function test_render_media() {
 		$widget = new AMP_Widget_Media_Audio();
-		$audio = '/tmp/small-audio.mp3';
+		$audio  = '/tmp/small-audio.mp3';
 		copy( DIR_TESTDATA . '/uploads/small-audio.mp3', $audio );
 		$attachment_id = self::factory()->attachment->create_object( array(
 			'file'           => $audio,