Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 18797)
+++ wp-includes/media.php	(working copy)
@@ -526,6 +526,13 @@
 	if ( !is_array( $imagedata = wp_get_attachment_metadata( $post_id ) ) )
 		return false;
 
+	// check the original image first!
+	if ( is_array( $size ) && ( ( $imagedata['width'] == $size[0] && $imagedata['height'] <= $size[1] ) || ( $imagedata['height'] == $size[1] && $imagedata['width'] <= $size[0] ) ) ) {
+		$file = basename( $imagedata['file'] );
+		list($width, $height) = image_constrain_size_for_editor( $imagedata['width'], $imagedata['height'], $size );
+		return compact( 'file', 'width', 'height' );
+	}
+	
 	// get the best one for a specified set of dimensions
 	if ( is_array($size) && !empty($imagedata['sizes']) ) {
 		foreach ( $imagedata['sizes'] as $_size => $data ) {