diff --git a/src/message.ts b/src/message.ts
index 07706fff..8882151d 100644
--- a/src/message.ts
+++ b/src/message.ts
@@ -122,8 +122,8 @@ export function isMessage(val: unknown): val is Message {
           hasOwnStringProperty(val, 'id') &&
           hasOwnObjectProperty(val, 'payload') &&
           // ExecutionResult
-          (hasOwnObjectProperty(val.payload, 'data') ||
-            hasOwnObjectProperty(val.payload, 'errors'))
+          (hasOwnProperty(val.payload, 'data') || // data
+            hasOwnObjectProperty(val.payload, 'errors')) // or error(s)
         );
       case MessageType.Error:
         return hasOwnStringProperty(val, 'id') && areGraphQLErrors(val.payload);