Index: src/wp-includes/class-wp-query.php
===================================================================
--- src/wp-includes/class-wp-query.php	(revision 55700)
+++ src/wp-includes/class-wp-query.php	(working copy)
@@ -2107,10 +2107,10 @@
 
 				if ( ! $ptype_obj->hierarchical ) {
 					// Non-hierarchical post types can directly use 'name'.
-					$q['name'] = $q[ $ptype_obj->query_var ];
+					$q['name'] = is_string( $q[ $ptype_obj->query_var ] ) ? $q[ $ptype_obj->query_var ] : '';
 				} else {
 					// Hierarchical post types will operate through 'pagename'.
-					$q['pagename'] = $q[ $ptype_obj->query_var ];
+					$q['pagename'] = is_string( $q[ $ptype_obj->query_var ] ) ? $q[ $ptype_obj->query_var ] : '';
 					$q['name']     = '';
 				}