Ticket #42416: 42416.diff

src/wp-includes/js/mce-view.js

@@ -863 +863 @@
 
                         // Obtain the target width for the embed.
                         if ( self.editor ) {
-                                maxwidth = self.editor.iframeElement.clientWidth - 20; // Minus the sum of horizontal margins and borders.
+                                maxwidth = self.editor.getBody().clientWidth;
                         }
 
                         wp.ajax.post( this.action, {