diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 596134f3c4..fc38abf01c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -66,6 +66,12 @@ jobs:
             - os: ubuntu-24.04
               python-version: '3.12'
               toxenv: py312-fuse3
+            - os: ubuntu-24.04
+              python-version: '3.13'
+              toxenv: py313-fuse3
+            - os: ubuntu-24.04
+              python-version: '3.14'
+              toxenv: py314-fuse3
             - os: macos-15
               python-version: '3.11'
               toxenv: py311-none  # note: no fuse testing, due to #6099, see also #6196.
diff --git a/setup.py b/setup.py
index 106139eef1..32ccb6d73b 100644
--- a/setup.py
+++ b/setup.py
@@ -63,8 +63,10 @@
 prefer_system_libxxhash = not bool(os.environ.get('BORG_USE_BUNDLED_XXHASH'))
 system_prefix_libxxhash = os.environ.get('BORG_LIBXXHASH_PREFIX')
 
-# Number of threads to use for cythonize, not used on windows
-cpu_threads = multiprocessing.cpu_count() if multiprocessing and multiprocessing.get_start_method() != 'spawn' else None
+# Number of threads to use for cythonize, not used on windows.
+# Only with the "fork" start method: "spawn" and "forkserver" (default on Linux since Python 3.14)
+# re-import setup.py in the worker processes, which recursively runs setup() there.
+cpu_threads = multiprocessing.cpu_count() if multiprocessing and multiprocessing.get_start_method() == 'fork' else None
 
 # Are we building on ReadTheDocs?
 on_rtd = os.environ.get('READTHEDOCS')
@@ -75,7 +77,7 @@
     # Please note:
     # using any other msgpack version is not supported by borg development and
     # any feedback related to issues caused by this will be ignored.
-    'msgpack >=0.5.6, <=1.1.1, !=1.0.1',
+    'msgpack >=0.5.6, <=1.2.4, !=1.0.1',
     'packaging',
 ]
 
@@ -297,6 +299,8 @@ def members_appended(*ds):
         'Programming Language :: Python :: 3.10',
         'Programming Language :: Python :: 3.11',
         'Programming Language :: Python :: 3.12',
+        'Programming Language :: Python :: 3.13',
+        'Programming Language :: Python :: 3.14',
         'Topic :: Security :: Cryptography',
         'Topic :: System :: Archiving :: Backup',
     ],
diff --git a/src/borg/archiver.py b/src/borg/archiver.py
index 971c3e7621..8374080e1d 100644
--- a/src/borg/archiver.py
+++ b/src/borg/archiver.py
@@ -1908,7 +1908,7 @@ def do_with_lock(self, args, repository):
             # any other mechanism relying on existing segment data not changing).
             # see issue #1867.
             repository.commit(compact=False)
-            return ret
+        return ret
 
     @with_repository(manifest=False, exclusive=True)
     def do_compact(self, args, repository):
diff --git a/src/borg/helpers/msgpack.py b/src/borg/helpers/msgpack.py
index 63561c9f42..327af646f6 100644
--- a/src/borg/helpers/msgpack.py
+++ b/src/borg/helpers/msgpack.py
@@ -182,7 +182,7 @@ def is_slow_msgpack():
 def is_supported_msgpack():
     # DO NOT CHANGE OR REMOVE! See also requirements and comments in setup.py.
     import msgpack
-    return (0, 5, 6) <= msgpack.version[:3] <= (1, 1, 1) and \
+    return (0, 5, 6) <= msgpack.version[:3] <= (1, 2, 4) and \
            msgpack.version not in [(1, 0, 1), ]  # < add bad releases here to deny list
 
 
diff --git a/src/borg/testsuite/repository.py b/src/borg/testsuite/repository.py
index ca0f9d9c07..70160ace62 100644
--- a/src/borg/testsuite/repository.py
+++ b/src/borg/testsuite/repository.py
@@ -977,7 +977,10 @@ def test_rpc_exception_transport(self):
             self.repository.call('inject_exception', {'kind': 'divide'})
         except RemoteRepository.RPCError as e:
             assert e.unpacked
-            assert e.get_message() == 'ZeroDivisionError: integer division or modulo by zero\n'
+            assert e.get_message() in (
+                'ZeroDivisionError: integer division or modulo by zero\n',  # Python < 3.14
+                'ZeroDivisionError: division by zero\n',  # Python >= 3.14
+            )
             assert e.exception_class == 'ZeroDivisionError'
             assert len(e.exception_full) > 0
 
diff --git a/tox.ini b/tox.ini
index 3ae0d53e6e..b7f4957fbb 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,7 +2,7 @@
 # fakeroot -u tox --recreate
 
 [tox]
-envlist = py{39,310,311,312}-{none,fuse2,fuse3}
+envlist = py{39,310,311,312,313,314}-{none,fuse2,fuse3}
 minversion = 3.2
 requires =
 	pkgconfig