diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -1281,7 +1281,7 @@
 )
 coreconfigitem(
     b'extensions',
-    b'.*',
+    b'[^:]*',
     default=None,
     generic=True,
 )
diff --git a/mercurial/extensions.py b/mercurial/extensions.py
--- a/mercurial/extensions.py
+++ b/mercurial/extensions.py
@@ -282,6 +282,7 @@
     result = ui.configitems(b"extensions")
     if whitelist is not None:
         result = [(k, v) for (k, v) in result if k in whitelist]
+    result = [(k, v) for (k, v) in result if b':' not in k]
     newindex = len(_order)
     ui.log(
         b'extension',