Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 23003)
+++ wp-includes/media.php	(working copy)
@@ -1832,7 +1832,7 @@
 						<#
 						var size = data.sizes['<?php echo esc_js( $value ); ?>'];
 						if ( size ) { #>
-							<option value="<?php echo esc_attr( $value ); ?>" <?php selected( $value, 'medium' ); ?>>
+							<option value="<?php echo esc_attr( $value ); ?>" <?php selected( $value, 'full' ); ?>>
 								<?php echo esc_html( $name ); ?> &ndash; {{ size.width }} &times; {{ size.height }}
 							</option>
 						<# } #>>