Index: src/wp-includes/query.php
===================================================================
--- src/wp-includes/query.php	(revision 26862)
+++ src/wp-includes/query.php	(working copy)
@@ -3265,6 +3265,9 @@
 		if ( $this->is_category || $this->is_tag || $this->is_tax ) {
 			if ( $this->is_category ) {
 				$term = get_term( $this->get( 'cat' ), 'category' );
+				if ( null == $term || is_wp_error( $term ) ) {
+					$term = get_term_by( 'name', $this->get( 'category_name' ), 'category' );
+				}
 			} elseif ( $this->is_tag ) {
 				$term = get_term( $this->get( 'tag_id' ), 'post_tag' );
 			} else {