diff --git src/wp-admin/js/widgets/media-widgets.js src/wp-admin/js/widgets/media-widgets.js
index cd03b09633..1408b35d01 100644
--- src/wp-admin/js/widgets/media-widgets.js
+++ src/wp-admin/js/widgets/media-widgets.js
@@ -142,9 +142,6 @@ wp.mediaWidgets = ( function( $ ) {
 					/**
 					 * Fetch media.
 					 *
-					 * This is a TEMPORARY measure until the WP API supports an oEmbed proxy endpoint. See #40450.
-					 *
-					 * @see https://core.trac.wordpress.org/ticket/40450
 					 * @returns {void}
 					 */
 					fetch: function() {
diff --git src/wp-includes/js/media-views.js src/wp-includes/js/media-views.js
index 1bdc6e6575..75cf452f50 100644
--- src/wp-includes/js/media-views.js
+++ src/wp-includes/js/media-views.js
@@ -4739,7 +4739,7 @@ EmbedUrl = View.extend({
 	},
 
 	url: function( event ) {
-		this.model.set( 'url', event.target.value );
+		this.model.set( 'url', $.trim( event.target.value ) );
 	},
 
 	/**
diff --git src/wp-includes/js/media/views/embed/url.js src/wp-includes/js/media/views/embed/url.js
index 3c99ca59ca..ab2863f1d0 100644
--- src/wp-includes/js/media/views/embed/url.js
+++ src/wp-includes/js/media/views/embed/url.js
@@ -60,7 +60,7 @@ EmbedUrl = View.extend({
 	},
 
 	url: function( event ) {
-		this.model.set( 'url', event.target.value );
+		this.model.set( 'url', $.trim( event.target.value ) );
 	},
 
 	/**