diff --git a/mercurial/wireprotoserver.py b/mercurial/wireprotoserver.py
index bbcaf3a74822b32de85c253934ef65dc86292c3f_bWVyY3VyaWFsL3dpcmVwcm90b3NlcnZlci5weQ==..7e19b640c53e44b07841194d621274d6197dcab6_bWVyY3VyaWFsL3dpcmVwcm90b3NlcnZlci5weQ== 100644
--- a/mercurial/wireprotoserver.py
+++ b/mercurial/wireprotoserver.py
@@ -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)
diff --git a/tests/test-bookmarks-corner-case.t b/tests/test-bookmarks-corner-case.t
index bbcaf3a74822b32de85c253934ef65dc86292c3f_dGVzdHMvdGVzdC1ib29rbWFya3MtY29ybmVyLWNhc2UudA==..7e19b640c53e44b07841194d621274d6197dcab6_dGVzdHMvdGVzdC1ib29rbWFya3MtY29ybmVyLWNhc2UudA== 100644
--- a/tests/test-bookmarks-corner-case.t
+++ b/tests/test-bookmarks-corner-case.t
@@ -200,4 +200,5 @@
   $ cat push-output.txt
   pushing to ssh://user@dummy/bookrace-server
   searching for changes
+  remote: setting raced push up
   remote has heads on branch 'default' that are not known locally: f26c3b5167d1
@@ -203,5 +204,4 @@
   remote has heads on branch 'default' that are not known locally: f26c3b5167d1
-  remote: setting raced push up
   remote: adding changesets
   remote: adding manifests
   remote: adding file changes
diff --git a/tests/test-ssh-proto.t b/tests/test-ssh-proto.t
index bbcaf3a74822b32de85c253934ef65dc86292c3f_dGVzdHMvdGVzdC1zc2gtcHJvdG8udA==..7e19b640c53e44b07841194d621274d6197dcab6_dGVzdHMvdGVzdC1zc2gtcHJvdG8udA== 100644
--- a/tests/test-ssh-proto.t
+++ b/tests/test-ssh-proto.t
@@ -104,6 +104,7 @@
   $ hg debugserve --sshstdio --logiofd 1 << EOF
   > hello
   > EOF
+  e> flush() -> None
   o> write(4) -> 4:
   o>     440\n
   o> write(440) -> 440:
@@ -119,6 +120,7 @@
   capabilities: batch branchmap $USUAL_BUNDLE2_CAPS$ changegroupsubset getbundle known lookup protocaps pushkey streamreqs=generaldelta,revlogv1,sparserevlog unbundle=HG10GZ,HG10BZ,HG10UN unbundlehash
 
   $ cat $TESTTMP/io
+  e> flush() -> None
   o> write(4) -> 4:
   o>     440\n
   o> write(440) -> 440: