diff --git a/edpop_explorer/sparqlreader.py b/edpop_explorer/sparqlreader.py
index b23dc10..2d6f969 100644
--- a/edpop_explorer/sparqlreader.py
+++ b/edpop_explorer/sparqlreader.py
@@ -91,7 +91,8 @@ def fetch(self) -> None:
         )
         # Call Reader's data conversion method to fill the record's Fields
         assert isinstance(self, Record)
-        self.from_reader._convert_record(self.original_graph, self)
+        assert issubclass(self.from_reader, SparqlReader)
+        self.from_reader.convert_record(self.original_graph, self)
 
         self.fetched = True