diff --git a/src/wp-includes/customize/class-wp-customize-site-icon-control.php b/src/wp-includes/customize/class-wp-customize-site-icon-control.php
index 7442fec..d5655de 100644
--- a/src/wp-includes/customize/class-wp-customize-site-icon-control.php
+++ b/src/wp-includes/customize/class-wp-customize-site-icon-control.php
@@ -60,6 +60,7 @@ class WP_Customize_Site_Icon_Control extends WP_Customize_Cropped_Image_Control
 		</label>
 
 		<# if ( data.attachment && data.attachment.id ) { #>
+		<# data.attachment.sizes = data.attachment.sizes || { 'full': { 'url': data.attachment.url } } #>
 			<div class="attachment-media-view">
 				<div class="site-icon-preview">
 					<div class="favicon-preview">