diff --git a/epanet/epanet.py b/epanet/epanet.py
index 10ea82b..0c2ba18 100644
--- a/epanet/epanet.py
+++ b/epanet/epanet.py
@@ -263,7 +263,7 @@ def run_project_return_dict(name: str, readable_output: bool = False) -> dict[st
     else:
         data['simulation_result'] = 'successful'
         if readable_output:
-            data |= _dump_output(opt)
+            data ['output'] = _dump_output(opt)
         else:
             data['output'] = dump_output_binary(opt)