diff --git a/src/__init__.py b/src/__init__.py
--- a/src/__init__.py
+++ b/src/__init__.py
@@ -38,8 +38,18 @@
 
 configtable = {}
 configitem = registrar.configitem(configtable)
-configitem('narrow', 'serveellipses',
+# Narrowhg *has* support for serving ellipsis nodes (which are used at
+# least by Google's internal server), but that support is pretty
+# fragile and has a lot of problems on real-world repositories that
+# have complex graph topologies. This could probably be corrected, but
+# absent someone needing the full support for ellipsis nodes in
+# repositories with merges, it's unlikely this work will get done. As
+# of this writining in late 2017, all repositories large enough for
+# ellipsis nodes to be a hard requirement also enforce strictly linear
+# history for other scaling reasons.
+configitem('experimental', 'narrowservebrokenellipses',
            default=False,
+           alias=[('narrow', 'serveellipses')],
 )
 
 # Export the commands table for Mercurial to see.
diff --git a/src/narrowbundle2.py b/src/narrowbundle2.py
--- a/src/narrowbundle2.py
+++ b/src/narrowbundle2.py
@@ -222,7 +222,7 @@
     include = sorted(filter(bool, kwargs.get('includepats', [])))
     exclude = sorted(filter(bool, kwargs.get('excludepats', [])))
     newmatch = narrowspec.match(repo.root, include=include, exclude=exclude)
-    if not repo.ui.configbool("narrow", "serveellipses"):
+    if not repo.ui.configbool("experimental", "narrowservebrokenellipses"):
         outgoing = exchange._computeoutgoing(repo, heads, common)
         if not outgoing.missing:
             return