diff --git a/event_model/__init__.py b/event_model/__init__.py
index b485ab36..b3380c86 100644
--- a/event_model/__init__.py
+++ b/event_model/__init__.py
@@ -2306,7 +2306,7 @@ def keys_without_stream_keys(dictionary, descriptor_data_keys):
     return [
         key for key in dictionary.keys() if (
             "external" not in descriptor_data_keys[key] or
-            descriptor_data_keys[key]["external"] != "STREAM:"
+            descriptor_data_keys[key]["external"] == "STREAM:"
         )
     ]