| Index: pkg/kernel/lib/type_environment.dart | 
| diff --git a/pkg/kernel/lib/type_environment.dart b/pkg/kernel/lib/type_environment.dart | 
| index 0b90cb4ba4742ec9856090ba65121553b44aaebf..8db70bb9374718e1cfe62a83712dddcc7f1021d5 100644 | 
| --- a/pkg/kernel/lib/type_environment.dart | 
| +++ b/pkg/kernel/lib/type_environment.dart | 
| @@ -145,6 +145,8 @@ abstract class SubtypeTester { | 
|  | 
| /// Returns true if [subtype] is a subtype of [supertype]. | 
| bool isSubtypeOf(DartType subtype, DartType supertype) { | 
| +    subtype = subtype.unalias; | 
| +    supertype = supertype.unalias; | 
| if (identical(subtype, supertype)) return true; | 
| if (subtype is BottomType) return true; | 
| if (supertype is DynamicType || | 
|  |