diff -r 3e91d9978bec -r 711ba0f1057e mercurial/unionrepo.py
--- a/mercurial/unionrepo.py	Fri Jan 15 01:58:59 2021 +0100
+++ b/mercurial/unionrepo.py	Wed Jan 20 14:47:13 2021 +0100
@@ -128,6 +128,7 @@
         deltas,
         linkmapper,
         transaction,
+        alwayscache=False,
         addrevisioncb=None,
         duplicaterevisioncb=None,
         maybemissingparents=False,