Index: wp-includes/class-wp-term-query.php
===================================================================
--- wp-includes/class-wp-term-query.php	(revision 38223)
+++ wp-includes/class-wp-term-query.php	(working copy)
@@ -331,6 +331,8 @@
 					$has_hierarchical_tax = true;
 				}
 			}
+		} else {
+			$has_hierarchical_tax = true;
 		}
 
 		if ( ! $has_hierarchical_tax ) {