diff --git a/hgext/fastannotate/__init__.py b/hgext/fastannotate/__init__.py
--- a/hgext/fastannotate/__init__.py
+++ b/hgext/fastannotate/__init__.py
@@ -100,8 +100,6 @@
 #
 # * rename the config knob for updating the local cache from a remote server
 #
-# * move various global-setup bits to extsetup() or reposetup()
-#
 # * move `flock` based locking to a common area
 #
 # * revise wireprotocol for sharing annotate files
@@ -185,7 +183,9 @@
     if ui.configbool('fastannotate', 'useflock', _flockavailable()):
         context.pathhelper.lock = context.pathhelper._lockflock
 
+def extsetup(ui):
     # fastannotate has its own locking, without depending on repo lock
+    # TODO: avoid mutating this unless the specific repo has it enabled
     localrepo.localrepository._wlockfreeprefix.add('fastannotate/')
 
 def reposetup(ui, repo):
diff --git a/hgext/fastannotate/protocol.py b/hgext/fastannotate/protocol.py
--- a/hgext/fastannotate/protocol.py
+++ b/hgext/fastannotate/protocol.py
@@ -223,5 +223,7 @@
     _registerwireprotocommand()
     if isinstance(repo, localrepo.localrepository):
         localreposetup(ui, repo)
+    # TODO: this mutates global state, but only if at least one repo
+    # has the extension enabled. This is probably bad for hgweb.
     if peersetup not in hg.wirepeersetupfuncs:
         hg.wirepeersetupfuncs.append(peersetup)