diff --git a/pyads/connection.py b/pyads/connection.py
index bfe4a55..d6f5ce4 100644
--- a/pyads/connection.py
+++ b/pyads/connection.py
@@ -598,8 +598,9 @@ def sum_read(port: int, adr: AmsAddr, data_names: List[str],
                                 list(structure_defs.keys()))  # type: ignore
 
             for data_name, structure_def in structure_defs.items():  # type: ignore
-                result[data_name] = dict_from_bytes(result[data_name],
-                                                    structure_def)  # type: ignore
+                if data_name in result:
+                    result[data_name] = dict_from_bytes(result[data_name],
+                        structure_def)
 
             return result
 
@@ -691,7 +692,7 @@ def write_by_name(
         return adsSyncWriteByNameEx(
             self._port, self._adr, data_name, value, plc_datatype, handle=handle
         )
-    
+
     def write_list_by_name(
             self,
             data_names_and_values: Dict[str, Any],