diff --git a/pomodoro_to_harvest.py b/pomodoro_to_harvest.py
index fb9a9b6..c129527 100644
--- a/pomodoro_to_harvest.py
+++ b/pomodoro_to_harvest.py
@@ -136,7 +136,7 @@ other_project_names = {
     "Personal": ["Personal/external", "Personal / external", "External"],
 }
 
-replacement_project_names = harvest_project_names.copy | other_project_names
+replacement_project_names = harvest_project_names | other_project_names
 
 for preferred, alternatives in replacement_project_names.items():
     # We compare all alternatives to lower case versions, and add the