diff -r fc1ba19ec4a0 -r c6d44457f7e3 mercurial/configitems.py
--- a/mercurial/configitems.py	Tue Nov 23 17:52:38 2021 -0800
+++ b/mercurial/configitems.py	Fri Nov 26 16:51:58 2021 +0100
@@ -1281,7 +1281,7 @@
 )
 coreconfigitem(
     b'extensions',
-    b'.*',
+    b'[^:]*',
     default=None,
     generic=True,
 )