diff --git a/src/wp-includes/class-wp-oembed-controller.php b/src/wp-includes/class-wp-oembed-controller.php
index e6dae0670d..63cc1842ed 100644
--- a/src/wp-includes/class-wp-oembed-controller.php
+++ b/src/wp-includes/class-wp-oembed-controller.php
@@ -153,7 +153,7 @@ final class WP_oEmbed_Controller {
 	 *
 	 * @see WP_oEmbed::get_html()
 	 * @param WP_REST_Request $request Full data about the request.
-	 * @return WP_Error|array oEmbed response data or WP_Error on failure.
+	 * @return object|WP_Error oEmbed response data or WP_Error on failure.
 	 */
 	public function get_proxy_item( $request ) {
 		$args = $request->get_params();
@@ -169,6 +169,14 @@ final class WP_oEmbed_Controller {
 		$url = $request['url'];
 		unset( $args['url'] );
 
+		// Copy maxwidth/maxheight to width/height since WP_oEmbed::fetch() uses these arg names.
+		if ( isset( $args['maxwidth'] ) ) {
+			$args['width'] = $args['maxwidth'];
+		}
+		if ( isset( $args['maxheight'] ) ) {
+			$args['height'] = $args['maxheight'];
+		}
+
 		$data = _wp_oembed_get_object()->get_data( $url, $args );
 
 		if ( false === $data ) {
diff --git a/tests/phpunit/tests/oembed/controller.php b/tests/phpunit/tests/oembed/controller.php
index ef6b42edd0..529811ceb8 100644
--- a/tests/phpunit/tests/oembed/controller.php
+++ b/tests/phpunit/tests/oembed/controller.php
@@ -49,7 +49,7 @@ class Test_oEmbed_Controller extends WP_UnitTestCase {
 	public function tearDown() {
 		parent::tearDown();
 
-		remove_filter( 'pre_http_request', array( $this, 'mock_embed_request' ), 10, 3 );
+		remove_filter( 'pre_http_request', array( $this, 'mock_embed_request' ), 10 );
 	}
 
 	/**
@@ -70,10 +70,12 @@ class Test_oEmbed_Controller extends WP_UnitTestCase {
 	public function mock_embed_request( $preempt, $r, $url ) {
 		unset( $preempt, $r );
 
+		$parsed_url = wp_parse_url( $url );
+		parse_str( $parsed_url['query'], $query_params );
 		$this->request_count += 1;
 
 		// Mock request to YouTube Embed.
-		if ( false !== strpos( $url, self::YOUTUBE_VIDEO_ID ) ) {
+		if ( ! empty( $query_params['url'] ) && false !== strpos( $query_params['url'], self::YOUTUBE_VIDEO_ID ) ) {
 			return array(
 				'response' => array(
 					'code' => 200,
@@ -84,14 +86,14 @@ class Test_oEmbed_Controller extends WP_UnitTestCase {
 						'type'             => 'video',
 						'provider_name'    => 'YouTube',
 						'provider_url'     => 'https://www.youtube.com',
-						'thumbnail_width'  => 480,
-						'width'            => 500,
-						'thumbnail_height' => 360,
-						'html'             => '<iframe width="500" height="375" src="https://www.youtube.com/embed/' . self::YOUTUBE_VIDEO_ID . '?feature=oembed" frameborder="0" allowfullscreen></iframe>',
+						'thumbnail_width'  => $query_params['maxwidth'],
+						'width'            => $query_params['maxwidth'],
+						'thumbnail_height' => $query_params['maxheight'],
+						'height'           => $query_params['maxheight'],
+						'html'             => '<iframe width="' . $query_params['maxwidth'] . '" height="' . $query_params['maxheight'] . '" src="https://www.youtube.com/embed/' . self::YOUTUBE_VIDEO_ID . '?feature=oembed" frameborder="0" allowfullscreen></iframe>',
 						'author_name'      => 'Yosemitebear62',
 						'thumbnail_url'    => 'https://i.ytimg.com/vi/' . self::YOUTUBE_VIDEO_ID . '/hqdefault.jpg',
 						'title'            => 'Yosemitebear Mountain Double Rainbow 1-8-10',
-						'height'           => 375,
 					)
 				),
 			);
@@ -477,13 +479,14 @@ class Test_oEmbed_Controller extends WP_UnitTestCase {
 		$response = $this->server->dispatch( $request );
 
 		$this->assertEquals( 400, $response->get_status() );
-		$data = $response->get_data();
 	}
 
 	public function test_proxy_with_valid_oembed_provider() {
 		wp_set_current_user( self::$editor );
 		$request = new WP_REST_Request( 'GET', '/oembed/1.0/proxy' );
 		$request->set_param( 'url', 'https://www.youtube.com/watch?v=' . self::YOUTUBE_VIDEO_ID );
+		$request->set_param( 'maxwidth', 456 );
+		$request->set_param( 'maxheight', 789 );
 		$request->set_param( '_wpnonce', wp_create_nonce( 'wp_rest' ) );
 		$response = $this->server->dispatch( $request );
 		$this->assertEquals( 200, $response->get_status() );
@@ -498,6 +501,8 @@ class Test_oEmbed_Controller extends WP_UnitTestCase {
 		$request = new WP_REST_Request( 'GET', '/oembed/1.0/proxy' );
 		$request->set_param( 'url', 'https://www.youtube.com/watch?v=' . self::YOUTUBE_VIDEO_ID );
 		$request->set_param( '_wpnonce', wp_create_nonce( 'wp_rest' ) );
+		$request->set_param( 'maxwidth', 456 );
+		$request->set_param( 'maxheight', 789 );
 		$response = $this->server->dispatch( $request );
 		$this->assertEquals( 1, $this->request_count );
 
@@ -508,6 +513,8 @@ class Test_oEmbed_Controller extends WP_UnitTestCase {
 		$this->assertTrue( is_object( $data ) );
 		$this->assertEquals( 'YouTube', $data->provider_name );
 		$this->assertEquals( 'https://i.ytimg.com/vi/' . self::YOUTUBE_VIDEO_ID . '/hqdefault.jpg', $data->thumbnail_url );
+		$this->assertEquals( $data->width, $request['maxwidth'] );
+		$this->assertEquals( $data->height, $request['maxheight'] );
 	}
 
 	public function test_proxy_with_invalid_oembed_provider_no_discovery() {