diff --git a/lib/eval/dart/service.dart b/lib/eval/dart/service.dart
index cccec457..b13366d3 100644
--- a/lib/eval/dart/service.dart
+++ b/lib/eval/dart/service.dart
@@ -23,7 +23,7 @@ class DartExtensionService implements ExtensionService {
 
     interpreter.execute(
       source: source.sourceCode!.replaceAll('Client(source)', 'Client()'),
-      args: source.toMSource(),
+      positionalArgs: [source.toMSource()],
     );
     return interpreter;
   }