diff --git src/wp-includes/customize/class-wp-customize-media-control.php src/wp-includes/customize/class-wp-customize-media-control.php
index bcd8db8..d306529 100644
--- src/wp-includes/customize/class-wp-customize-media-control.php
+++ src/wp-includes/customize/class-wp-customize-media-control.php
@@ -158,8 +158,10 @@ class WP_Customize_Media_Control extends WP_Customize_Control {
 				<div class="container">
 					<div class="attachment-media-view attachment-media-view-{{ data.attachment.type }} {{ data.attachment.orientation }}">
 						<div class="thumbnail thumbnail-{{ data.attachment.type }}">
-							<# if ( 'image' === data.attachment.type && data.attachment.sizes && data.attachment.sizes.medium ) { #>
-								<img class="attachment-thumb" src="{{ data.attachment.sizes.medium.url }}" draggable="false" alt="" />
+							<# if ( 'image' === data.attachment.type && data.attachment.sizes && data.attachment.sizes.medium && data.attachment.sizes.large && data.attachment.sizes.full ) { #>
+								<img class="attachment-thumb" src="{{ data.attachment.sizes.medium.url }}" srcset="{{ data.attachment.sizes.medium.url }} {{ data.attachment.sizes.medium.width }}w, {{ data.attachment.sizes.large.url }} {{ data.attachment.sizes.large.width }}w, {{ data.attachment.sizes.full.url }} {{ data.attachment.sizes.full.width }}w" sizes="(max-width: 640px) calc(100vw - 24px), 273px" draggable="false" alt="" />
+							<# } else if ( 'image' === data.attachment.type && data.attachment.sizes && data.attachment.sizes.medium && data.attachment.sizes.full ) { #>
+								<img class="attachment-thumb" src="{{ data.attachment.sizes.medium.url }}" srcset="{{ data.attachment.sizes.medium.url }} {{ data.attachment.sizes.medium.width }}w, {{ data.attachment.sizes.full.url }} {{ data.attachment.sizes.full.width }}w"  sizes="(max-width: 640px) calc(100vw - 24px), 273px" draggable="false" alt="" />
 							<# } else if ( 'image' === data.attachment.type && data.attachment.sizes && data.attachment.sizes.full ) { #>
 								<img class="attachment-thumb" src="{{ data.attachment.sizes.full.url }}" draggable="false" alt="" />
 							<# } else if ( 'audio' === data.attachment.type ) { #>