diff -r bd3cb917761a -r 2406dbba49bd mercurial/server.py
--- a/mercurial/server.py	Fri Mar 31 23:00:41 2017 -0400
+++ b/mercurial/server.py	Sat Apr 15 18:05:40 2017 -0400
@@ -15,6 +15,7 @@
 
 from . import (
     chgserver,
+    cmdutil,
     commandserver,
     error,
     hgweb,
@@ -130,11 +131,22 @@
         baseui = ui
     webconf = opts.get('web_conf') or opts.get('webdir_conf')
     if webconf:
+        if opts.get('subrepos'):
+            raise error.Abort(_('--web-conf cannot be used with --subrepos'))
+
         # load server settings (e.g. web.port) to "copied" ui, which allows
         # hgwebdir to reload webconf cleanly
         servui = ui.copy()
         servui.readconfig(webconf, sections=['web'])
         alluis.add(servui)
+    elif opts.get('subrepos'):
+        servui = ui
+
+        # If repo is None, hgweb.createapp() already raises a proper abort
+        # message as long as webconf is None.
+        if repo:
+            webconf = dict()
+            cmdutil.addwebdirpath(repo, "", webconf)
     else:
         servui = ui