diff --git a/lib/src/front_end/piece_factory.dart b/lib/src/front_end/piece_factory.dart
index 84462c90..cba03ac9 100644
--- a/lib/src/front_end/piece_factory.dart
+++ b/lib/src/front_end/piece_factory.dart
@@ -837,8 +837,6 @@ mixin PieceFactory {
               tokenPiece(combinatorNode.keyword),
               for (var name in names) tokenPiece(name.token, commaAfter: true),
             ]));
-          default:
-            throw StateError('Unknown combinator type $combinatorNode.');
         }
       }