diff --git a/mercurial/transaction.py b/mercurial/transaction.py
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_bWVyY3VyaWFsL3RyYW5zYWN0aW9uLnB5..63dc24be635d2144538323d88535d6b4e552c668_bWVyY3VyaWFsL3RyYW5zYWN0aW9uLnB5 100644
--- a/mercurial/transaction.py
+++ b/mercurial/transaction.py
@@ -409,7 +409,7 @@
 
         vfs = self._vfsmap[location]
         dirname, filename = vfs.split(file)
-        backupfilename = b"%s.backup.%s" % (self._journal, filename)
+        backupfilename = b"%s.backup.%s.bck" % (self._journal, filename)
         backupfile = vfs.reljoin(dirname, backupfilename)
         if vfs.exists(file):
             filepath = vfs.join(file)
diff --git a/tests/test-fncache.t b/tests/test-fncache.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC1mbmNhY2hlLnQ=..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC1mbmNhY2hlLnQ= 100644
--- a/tests/test-fncache.t
+++ b/tests/test-fncache.t
@@ -104,7 +104,7 @@
   .hg/phaseroots
   .hg/requires
   .hg/undo
-  .hg/undo.backup.branch
+  .hg/undo.backup.branch.bck
   .hg/undo.backupfiles
   .hg/undo.desc
   .hg/wcache
@@ -144,7 +144,7 @@
   .hg/store/requires
   .hg/store/undo
   .hg/store/undo.backupfiles
-  .hg/undo.backup.branch
+  .hg/undo.backup.branch.bck
   .hg/undo.desc
   .hg/wcache
   .hg/wcache/checkisexec (execbit !)
diff --git a/tests/test-hardlinks.t b/tests/test-hardlinks.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC1oYXJkbGlua3MudA==..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC1oYXJkbGlua3MudA== 100644
--- a/tests/test-hardlinks.t
+++ b/tests/test-hardlinks.t
@@ -52,7 +52,7 @@
   1 r1/.hg/store/phaseroots
   1 r1/.hg/store/requires
   1 r1/.hg/store/undo
-  1 r1/.hg/store/undo.backup.fncache (repofncache !)
+  1 r1/.hg/store/undo.backup.fncache.bck (repofncache !)
   1 r1/.hg/store/undo.backupfiles
 
 
@@ -93,7 +93,7 @@
   1 r1/.hg/store/phaseroots
   1 r1/.hg/store/requires
   1 r1/.hg/store/undo
-  1 r1/.hg/store/undo.backup.fncache (repofncache !)
+  1 r1/.hg/store/undo.backup.fncache.bck (repofncache !)
   1 r1/.hg/store/undo.backupfiles
 
   $ nlinksdir r2/.hg/store
@@ -252,8 +252,8 @@
   2 r4/.hg/store/requires
   2 r4/.hg/store/undo
   2 r4/.hg/store/undo.backupfiles
-  [24] r4/.hg/undo.backup.branch (re)
-  2 r4/\.hg/undo\.backup\.dirstate (re)
+  [24] r4/.hg/undo.backup.branch.bck (re)
+  2 r4/\.hg/undo\.backup\.dirstate.bck (re)
   2 r4/.hg/undo.desc
   2 r4/.hg/wcache/checkisexec (execbit !)
   2 r4/.hg/wcache/checklink-target (symlink !)
@@ -266,5 +266,5 @@
 
 Update back to revision 12 in r4 should break hardlink of file f1 and f3:
 #if hardlink-whitelisted
-  $ nlinksdir r4/.hg/undo.backup.dirstate r4/.hg/dirstate
+  $ nlinksdir r4/.hg/undo.backup.dirstate.bck r4/.hg/dirstate
   2 r4/.hg/dirstate
@@ -270,5 +270,5 @@
   2 r4/.hg/dirstate
-  2 r4/.hg/undo.backup.dirstate
+  2 r4/.hg/undo.backup.dirstate.bck
 #endif
 
 
@@ -305,8 +305,8 @@
   2 r4/.hg/store/requires
   2 r4/.hg/store/undo
   2 r4/.hg/store/undo.backupfiles
-  [23] r4/.hg/undo.backup.branch (re)
-  2 r4/\.hg/undo\.backup\.dirstate (re)
+  [23] r4/.hg/undo.backup.branch.bck (re)
+  2 r4/\.hg/undo\.backup\.dirstate.bck (re)
   2 r4/.hg/undo.desc
   2 r4/.hg/wcache/checkisexec (execbit !)
   2 r4/.hg/wcache/checklink-target (symlink !)
@@ -319,5 +319,5 @@
   2 r4/f3 (no-execbit !)
 
 #if hardlink-whitelisted
-  $ nlinksdir r4/.hg/undo.backup.dirstate r4/.hg/dirstate
+  $ nlinksdir r4/.hg/undo.backup.dirstate.bck r4/.hg/dirstate
   1 r4/.hg/dirstate
@@ -323,5 +323,5 @@
   1 r4/.hg/dirstate
-  2 r4/.hg/undo.backup.dirstate
+  2 r4/.hg/undo.backup.dirstate.bck
 #endif
 
 Test hardlinking outside hg:
diff --git a/tests/test-hook.t b/tests/test-hook.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC1ob29rLnQ=..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC1ob29rLnQ= 100644
--- a/tests/test-hook.t
+++ b/tests/test-hook.t
@@ -465,7 +465,7 @@
   phaseroots
   requires
   undo
-  undo.backup.fncache (repofncache !)
+  undo.backup.fncache.bck (repofncache !)
   undo.backupfiles
 
 
diff --git a/tests/test-inherit-mode.t b/tests/test-inherit-mode.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC1pbmhlcml0LW1vZGUudA==..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC1pbmhlcml0LW1vZGUudA== 100644
--- a/tests/test-inherit-mode.t
+++ b/tests/test-inherit-mode.t
@@ -95,7 +95,7 @@
   00600 ./.hg/store/requires
   00660 ./.hg/store/undo
   00660 ./.hg/store/undo.backupfiles
-  00660 ./.hg/undo.backup.branch
+  00660 ./.hg/undo.backup.branch.bck
   00660 ./.hg/undo.desc
   00770 ./.hg/wcache/
   00711 ./.hg/wcache/checkisexec
@@ -153,7 +153,7 @@
   00660 ../push/.hg/store/requires
   00660 ../push/.hg/store/undo
   00660 ../push/.hg/store/undo.backupfiles
-  00660 ../push/.hg/undo.backup.branch
+  00660 ../push/.hg/undo.backup.branch.bck
   00660 ../push/.hg/undo.desc
   00770 ../push/.hg/wcache/
 
diff --git a/tests/test-largefiles-cache.t b/tests/test-largefiles-cache.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC1sYXJnZWZpbGVzLWNhY2hlLnQ=..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC1sYXJnZWZpbGVzLWNhY2hlLnQ= 100644
--- a/tests/test-largefiles-cache.t
+++ b/tests/test-largefiles-cache.t
@@ -184,7 +184,7 @@
 
   $ find share_dst/.hg/largefiles/* | sort
   share_dst/.hg/largefiles/dirstate
-  share_dst/.hg/largefiles/undo.backup.dirstate
+  share_dst/.hg/largefiles/undo.backup.dirstate.bck
 
   $ find src/.hg/largefiles/* | egrep "(dirstate|$hash)" | sort
   src/.hg/largefiles/dirstate
diff --git a/tests/test-persistent-nodemap.t b/tests/test-persistent-nodemap.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC1wZXJzaXN0ZW50LW5vZGVtYXAudA==..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC1wZXJzaXN0ZW50LW5vZGVtYXAudA== 100644
--- a/tests/test-persistent-nodemap.t
+++ b/tests/test-persistent-nodemap.t
@@ -1193,8 +1193,6 @@
 (note: the stream clone code wronly pick the `undo.` files)
 
   $ cat clone-output-2
-  adding [s] undo.backup.00manifest.n (62 bytes) (known-bad-output !)
-  adding [s] undo.backup.00changelog.n (62 bytes) (known-bad-output !)
   adding [s] 00manifest.n (62 bytes)
   adding [s] 00manifest-*.nd (118 KB) (glob)
   adding [s] 00changelog.n (62 bytes)
diff --git a/tests/test-rebase-abort.t b/tests/test-rebase-abort.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC1yZWJhc2UtYWJvcnQudA==..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC1yZWJhc2UtYWJvcnQudA== 100644
--- a/tests/test-rebase-abort.t
+++ b/tests/test-rebase-abort.t
@@ -392,7 +392,6 @@
   .hg/dirstate
   .hg/merge/state
   .hg/rebasestate
-  .hg/undo.backup.dirstate
   .hg/updatestate
 
   $ hg rebase -s 3 -d tip
diff --git a/tests/test-rollback.t b/tests/test-rollback.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC1yb2xsYmFjay50..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC1yb2xsYmFjay50 100644
--- a/tests/test-rollback.t
+++ b/tests/test-rollback.t
@@ -72,7 +72,7 @@
   $ hg update bar
   1 files updated, 0 files merged, 1 files removed, 0 files unresolved
   (activating bookmark bar)
-  $ cat .hg/undo.backup.branch
+  $ cat .hg/undo.backup.branch.bck
   test
   $ hg log -G --template '{rev}  [{branch}] ({bookmarks}) {desc|firstline}\n'
   o  2  [test] (foo) add b
diff --git a/tests/test-transaction-rollback-on-revlog-split.t b/tests/test-transaction-rollback-on-revlog-split.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC10cmFuc2FjdGlvbi1yb2xsYmFjay1vbi1yZXZsb2ctc3BsaXQudA==..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC10cmFuc2FjdGlvbi1yb2xsYmFjay1vbi1yZXZsb2ctc3BsaXQudA== 100644
--- a/tests/test-transaction-rollback-on-revlog-split.t
+++ b/tests/test-transaction-rollback-on-revlog-split.t
@@ -172,7 +172,7 @@
   data/file.i 1174
   data/file.d 0
   $ cat .hg/store/journal.backupfiles | tr -s '\000' ' ' | tr -s '\00' ' '| grep data/file
-   data/file.i data/journal.backup.file.i 0
+   data/file.i data/journal.backup.file.i.bck 0
    data/file.i.s 0
 
 recover is rolling the split back, the fncache is still valid
diff --git a/tests/test-upgrade-repo.t b/tests/test-upgrade-repo.t
index a52aae8bcc7ac5d9dfe2c12cd4b433a8e6c8d62d_dGVzdHMvdGVzdC11cGdyYWRlLXJlcG8udA==..63dc24be635d2144538323d88535d6b4e552c668_dGVzdHMvdGVzdC11cGdyYWRlLXJlcG8udA== 100644
--- a/tests/test-upgrade-repo.t
+++ b/tests/test-upgrade-repo.t
@@ -866,7 +866,7 @@
   phaseroots
   requires
   undo
-  undo.backup.fncache
+  undo.backup.fncache.bck
   undo.backupfiles
 
 unless --no-backup is passed