diff --git a/common/python/nomadcore/parser_backend.py b/common/python/nomadcore/parser_backend.py
index 92687d4e4ff9bcbe326660c9729da74a8c04cd18..8ce94e5f7ef321fa3d321db5299c43201e7cfb0c 100644
--- a/common/python/nomadcore/parser_backend.py
+++ b/common/python/nomadcore/parser_backend.py
@@ -245,7 +245,7 @@ class JsonParseEventsWriterBackend(object):
             'lineNr': match_telemetry['lineNr'],
             'matcherName': match_telemetry['matcherName'],
             'matchFlags': match_telemetry['matchFlags'],
-            'flat_values': match_telemetry['span_flat'],
+            'flatValues': match_telemetry['span_flat'],
             'group': match_telemetry['group'],
         }
         self.__jsonOutput(res)