--- a/mercurial/wireprotoserver.py	Sun Sep 08 00:11:20 2019 +0200
+++ b/mercurial/wireprotoserver.py	Sun Sep 08 01:02:34 2019 +0200
@@ -657,6 +657,8 @@
                 continue
 
             rsp = wireprotov1server.dispatch(repo, proto, request)
+            repo.ui.fout.flush()
+            repo.ui.ferr.flush()
 
             if isinstance(rsp, bytes):
                 _sshv1respondbytes(fout, rsp)