diff -r e743907d0932 -r d5498db5f86a mercurial/wireprotoserver.py
--- a/mercurial/wireprotoserver.py	Sun Sep 30 16:11:35 2018 +0900
+++ b/mercurial/wireprotoserver.py	Sun Sep 30 03:42:35 2018 +0530
@@ -38,6 +38,8 @@
 HGTYPE2 = 'application/mercurial-0.2'
 HGERRTYPE = 'application/hg-error'
 
+NARROWCAP = 'exp-narrow-1'
+
 SSHV1 = wireprototypes.SSHV1
 SSHV2 = wireprototypes.SSHV2