diff --git a/dwds/lib/src/debugging/instance.dart b/dwds/lib/src/debugging/instance.dart
index 27fa81a1b..bc6f5f3a4 100644
--- a/dwds/lib/src/debugging/instance.dart
+++ b/dwds/lib/src/debugging/instance.dart
@@ -268,7 +268,9 @@ class InstanceHelper extends Domain {
       objectId,
       offset: offset,
       count: count,
-      length: metaData.length,
+      length: metaData.kind != InstanceKind.kPlainInstance
+          ? metaData.length
+          : null,
     );
 
     final dartProperties = await _dartFieldsFor(properties, remoteObject);