diff --git a/mercurial/hgweb/hgweb_mod.py b/mercurial/hgweb/hgweb_mod.py
--- a/mercurial/hgweb/hgweb_mod.py
+++ b/mercurial/hgweb/hgweb_mod.py
@@ -22,6 +22,7 @@ from .common import (
 from .. import (
     encoding,
     error,
+    extensions,
     formatter,
     hg,
     hook,
@@ -212,6 +213,7 @@ class hgweb(object):
                 u = baseui.copy()
             else:
                 u = uimod.ui.load()
+                extensions.loadall(u)
             r = hg.repository(u, repo)
         else:
             # we trust caller to give us a private copy
diff --git a/mercurial/hgweb/hgwebdir_mod.py b/mercurial/hgweb/hgwebdir_mod.py
--- a/mercurial/hgweb/hgwebdir_mod.py
+++ b/mercurial/hgweb/hgwebdir_mod.py
@@ -30,6 +30,7 @@ from .. import (
     configitems,
     encoding,
     error,
+    extensions,
     hg,
     profiling,
     pycompat,
@@ -268,6 +269,9 @@ class hgwebdir(object):
         self.lastrefresh = 0
         self.motd = None
         self.refresh()
+        if not baseui:
+            # set up environment for new ui
+            extensions.loadall(self.ui)
 
     def refresh(self):
         if self.ui: