
$title
diff --git a/archivebox/util.py b/archivebox/util.py
index 43b5c7c0..ec8c256b 100644
--- a/archivebox/util.py
+++ b/archivebox/util.py
@@ -450,7 +450,7 @@ def merge_links(a: Link, b: Link) -> Link:
sources = list(set(a.sources + b.sources))
- all_methods = (set(a.history.keys()) | set(a.history.keys()))
+ all_methods = set(list(a.history.keys()) + list(a.history.keys()))
history = {
method: (a.history.get(method) or []) + (b.history.get(method) or [])
for method in all_methods