diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2d18ec53dc..71150412bf 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -451,6 +451,12 @@ jobs:
             pyver: '3.13'
             do_binaries: false
 
+          - os: haiku
+            version: 'r1beta6'
+            display_name: Haiku
+            pyver: '3.14'
+            do_binaries: false
+
     steps:
       - name: Check out repository
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
@@ -474,7 +480,7 @@ jobs:
         # a normal boot takes < 1 minute; since 1.4.0 the action bounds
         # waiting for boot itself, this is just an additional safety net.
         timeout-minutes: 15
-        uses: cross-platform-actions/action@24ef01df165c76df1ed2b9f9e9212e78dc2fc963  # v1.4.0
+        uses: cross-platform-actions/action@faa0c6197e94aacf1c5956460152c8380d3560a5  # v1.5.0
         with:
           operating_system: ${{ matrix.os }}
           version: ${{ matrix.version }}
@@ -641,13 +647,11 @@ jobs:
 
             haiku)
               pkgman refresh
-              pkgman install -y git pkgconfig lz4
-              pkgman install -y openssl3
-              pkgman install -y rust_bin
-              pkgman install -y python3.11
+              # already installed:
+              # pkgman install -y git pkgconfig lz4 openssl3
               pkgman install -y lz4_devel openssl3_devel
+              pkgman install -y rust_bin
 
-              # there is no pkgman package for tox, so we install it into a venv
               python3 -m ensurepip --upgrade
               python3 -m pip install --upgrade pip wheel
               python3 -m venv .venv
@@ -656,8 +660,31 @@ jobs:
               export PKG_CONFIG_PATH="/system/develop/lib/pkgconfig:/system/lib/pkgconfig:${PKG_CONFIG_PATH:-}"
               export BORG_LIBLZ4_PREFIX=/system/develop
               export BORG_OPENSSL_PREFIX=/system/develop
-              pip install -r requirements.d/development.lock.txt
-              pip install -e .
+
+              # this VM corrupts data every now and then: rustc crashed on crate metadata it
+              # had written itself ("assertion failed: bytes[len] == STR_SENTINEL") and pip
+              # found sha256 mismatches reading big wheels back from its own cache. Build
+              # outside /boot/system/cache/tmp (haiku's /tmp) and run one rustc at a time,
+              # in case that corruption comes from disk or memory pressure.
+              export TMPDIR=/boot/home/borg-tmp
+              mkdir -p "$TMPDIR"
+              export CARGO_TARGET_DIR="$TMPDIR/cargo-target"
+              export CARGO_BUILD_JOBS=1
+
+              # retry a pip install that hit a corrupted file, dropping the cached (possibly
+              # corrupted) files first, so one of them does not fail the whole job - and does
+              # not end up in the actions cache, failing every following run, too.
+              pip_install() {
+                for attempt in 1 2 3; do
+                  pip install "$@" && return 0
+                  echo "*** pip install failed (attempt $attempt), purging the pip cache and retrying ***"
+                  pip cache purge || true
+                done
+                return 1
+              }
+
+              pip_install -r requirements.d/development.lock.txt
+              pip_install -e .
 
               # troubles with either tox or pytest xdist, so we run pytest manually:
               pytest -v -n auto -rs --cov=borg --cov-config=pyproject.toml --cov-report=xml --junitxml=test-results.xml --benchmark-skip -k "not remote and not socket"
diff --git a/pyproject.toml b/pyproject.toml
index a80a756a59..4ce900721d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -46,6 +46,8 @@ dependencies = [
   "blake3 >= 1.0; sys_platform != 'win32'",
   "blake3 >= 1.0,!=1.0.9; sys_platform == 'win32'",  # 1.0.9 does not build on windows/msys2/mingw
   "tzdata; sys_platform == 'win32'",  # zoneinfo has no system tz database on Windows (date: named zones)
+  # same on haiku (sys.platform is 'haiku1' on pythons older than 3.13)
+  "tzdata; sys_platform == 'haiku' or sys_platform == 'haiku1'",
 ]
 
 [project.optional-dependencies]
diff --git a/src/borg/conftest.py b/src/borg/conftest.py
index fd20dfe3f3..9925ee9d29 100644
--- a/src/borg/conftest.py
+++ b/src/borg/conftest.py
@@ -84,6 +84,10 @@ def clean_env(tmpdir_factory, monkeypatch):
     keys = [key for key in os.environ if key.startswith("BORG_") and key not in ("BORG_FUSE_IMPL",)]
     for key in keys:
         monkeypatch.delenv(key, raising=False)
+    # a "borg serve" started by a test must not mistake the ssh forced command of the session
+    # the tests happen to run in (e.g. a CI runner driven over ssh) for the command line of a
+    # borg client - it would fail to parse it and exit before serving anything.
+    monkeypatch.delenv("SSH_ORIGINAL_COMMAND", raising=False)
     # avoid that we access / modify the user's normal .config / .cache directory:
     base_dir = tmpdir_factory.mktemp("borg-base-dir")
     monkeypatch.setenv("BORG_BASE_DIR", str(base_dir))
diff --git a/src/borg/fslocking.py b/src/borg/fslocking.py
index 5a7f241ea0..13bba12df2 100644
--- a/src/borg/fslocking.py
+++ b/src/borg/fslocking.py
@@ -220,6 +220,11 @@ def kill_stale_lock(self):
             return False
         except PermissionError:  # win32 might throw this.
             return False
+        except OSError:
+            # we can not read the lock directory - e.g. haiku fails this with EBUSY or
+            # "bad data" while the directory is concurrently replaced via rename().
+            # Not being able to look at the lock means we can not call it stale, see by_me().
+            return False
         else:
             for name in names:
                 try:
diff --git a/src/borg/helpers/fs.py b/src/borg/helpers/fs.py
index e7a3d44ebf..3225bf8277 100644
--- a/src/borg/helpers/fs.py
+++ b/src/borg/helpers/fs.py
@@ -16,7 +16,7 @@
 from .errors import Error
 
 from .process import prepare_subprocess_env
-from ..platformflags import is_win32
+from ..platformflags import is_win32, is_haiku
 
 from ..constants import *  # NOQA
 
@@ -614,6 +614,13 @@ def read(self, size):
                 data = os.read(self.fd, remaining)
             except BlockingIOError:
                 data = None  # a writer is connected, but no data is available right now
+            except OSError as err:
+                if is_haiku and err.errno == errno.ENOMEM:
+                    # haiku fails a read from a fifo nobody has opened for writing with ENOMEM
+                    # instead of returning b"" - it means the same here: no writer (yet).
+                    data = b""
+                else:
+                    raise
             if data:
                 parts.append(data)
                 remaining -= len(data)
diff --git a/src/borg/legacy/remote.py b/src/borg/legacy/remote.py
index 93a5c9dbfb..cef1be02cc 100644
--- a/src/borg/legacy/remote.py
+++ b/src/borg/legacy/remote.py
@@ -29,7 +29,7 @@
 from ..repository import Repository, StoreObjectNotFound
 from ..version import parse_version, format_version
 from ..helpers.datastruct import EfficientCollectionQueue
-from ..platform import is_win32
+from ..platform import is_win32, is_haiku
 
 logger = create_logger(__name__)
 
@@ -249,7 +249,10 @@ def __init__(self, location, create=False, exclusive=False, lock_wait=None, lock
             self.stdout_fd = self.p.stdout.fileno()
             self.stderr_fd = self.p.stderr.fileno()
             self.r_fds = [self.stdout_fd, self.stderr_fd]
-            self.x_fds = [self.stdin_fd, self.stdout_fd, self.stderr_fd]
+            # haiku's select() reports pipes in the exceptional set although nothing is wrong,
+            # so do not watch for exceptional conditions there - a broken pipe still shows up
+            # as a read/write error below.
+            self.x_fds = [] if is_haiku else [self.stdin_fd, self.stdout_fd, self.stderr_fd]
         else:
             raise Error(f"Unsupported protocol {location.proto}")
 
diff --git a/src/borg/testsuite/archiver/webdav_cmd_test.py b/src/borg/testsuite/archiver/webdav_cmd_test.py
index 5457b41fd5..7b6f957265 100644
--- a/src/borg/testsuite/archiver/webdav_cmd_test.py
+++ b/src/borg/testsuite/archiver/webdav_cmd_test.py
@@ -84,15 +84,30 @@ def webdav_server(archiver):
             thread.join(timeout=10)
 
 
+def urlopen(request, attempts=10):
+    """urllib.request.urlopen, but retry a connect that fails with EWOULDBLOCK.
+
+    haiku fails connecting to a listening localhost socket with EWOULDBLOCK (rather than
+    waiting for the server to accept) when the server does not accept immediately.
+    """
+    for attempt in range(attempts):
+        try:
+            return urllib.request.urlopen(request)
+        except urllib.error.URLError as err:
+            if not isinstance(err.reason, BlockingIOError) or attempt == attempts - 1:
+                raise
+            time.sleep(0.1)
+
+
 def get(url, headers=None):
     request = urllib.request.Request(url, headers=headers or {})
-    with urllib.request.urlopen(request) as response:
+    with urlopen(request) as response:
         return response.status, dict(response.headers), response.read()
 
 
 def http_request(url, method, headers=None, body=None):
     req = urllib.request.Request(url, data=body, method=method, headers=headers or {})
-    with urllib.request.urlopen(req) as response:
+    with urlopen(req) as response:
         return response.status, dict(response.headers), response.read()
 
 
@@ -300,7 +315,7 @@ def test_webdav_errors(archivers, request):
             get(base_url + "/test/input/../input/file1")
         assert exc_info.value.code == 404
         with pytest.raises(urllib.error.HTTPError) as exc_info:
-            urllib.request.urlopen(urllib.request.Request(base_url + "/", method="POST"))
+            urlopen(urllib.request.Request(base_url + "/", method="POST"))
         assert exc_info.value.code == 405
         # writing/locking WebDAV methods are rejected, too
         for method in "PUT", "MKCOL", "LOCK", "PROPPATCH":