diff --git src/wp-includes/theme-compat/embed-content.php src/wp-includes/theme-compat/embed-content.php
index 05498eb..fca4f38 100644
--- src/wp-includes/theme-compat/embed-content.php
+++ src/wp-includes/theme-compat/embed-content.php
@@ -27,7 +27,7 @@
 		$image_size   = 'full'; // Fallback.
 
 		$meta = wp_get_attachment_metadata( $thumbnail_id );
-		if ( is_array( $meta ) ) {
+		if ( ! empty( $meta['sizes'] ) ) {
 			foreach ( $meta['sizes'] as $size => $data ) {
 				if ( $data['width'] / $data['height'] > $aspect_ratio ) {
 					$aspect_ratio = $data['width'] / $data['height'];