diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9129072bd..547955118 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -540,6 +540,12 @@ jobs:
                 sudo python3 -m ensurepip
                 sudo python3 -m pip install virtualenv
 
+                # On omniOS /tmp is swap-backed tmpfs (small, RAM-bound), so the pip/cargo
+                # build temps and the pytest temp tree quickly exhaust it ("no space left on
+                # device"). /var/tmp is disk-backed (ZFS), so redirect TMPDIR there.
+                export TMPDIR=/var/tmp/borg-ci
+                mkdir -p "$TMPDIR"
+
                 python3 -m venv .venv
                 . .venv/bin/activate
                 python -V
diff --git a/src/borg/testsuite/archiver/extract_cmd_test.py b/src/borg/testsuite/archiver/extract_cmd_test.py
index c65f385f1..7a19d46b5 100644
--- a/src/borg/testsuite/archiver/extract_cmd_test.py
+++ b/src/borg/testsuite/archiver/extract_cmd_test.py
@@ -833,7 +833,14 @@ def test_extract_y2261(archivers, request):
     create_regular_file(archiver.input_path, "file_y2261", contents=b"post y2038 test")
     # 2261-01-01 00:00:00 UTC as a Unix timestamp (seconds).
     time_y2261 = 9183110400
-    os.utime("input/file_y2261", (time_y2261, time_y2261))
+    try:
+        os.utime("input/file_y2261", (time_y2261, time_y2261))
+    except OSError as e:
+        if e.errno == errno.EOVERFLOW:
+            # some filesystems/platforms cannot store timestamps beyond y2038
+            # (e.g. ZFS on omniOS rejects this with EOVERFLOW).
+            pytest.skip("filesystem cannot store post-y2038 timestamps")
+        raise
     cmd(archiver, "repo-create", RK_ENCRYPTION)
     cmd(archiver, "create", "test", "input")
     with changedir("output"):
diff --git a/src/borg/testsuite/helpers/fs_test.py b/src/borg/testsuite/helpers/fs_test.py
index ae3af53d2..dcad7969b 100644
--- a/src/borg/testsuite/helpers/fs_test.py
+++ b/src/borg/testsuite/helpers/fs_test.py
@@ -242,6 +242,7 @@ def test_get_runtime_dir(monkeypatch):
             os.path.join("/var/run/user", uid, "borg"),
             os.path.join(f"/tmp/runtime-{uid}", "borg"),
             os.path.join(f"/mnt/eafs/tmp/runtime-{uid}", "borg"),  # CI netbsd
+            os.path.join(f"/var/tmp/borg-ci/runtime-{uid}", "borg"),  # CI omnios (TMPDIR)
         ]
         monkeypatch.setenv("XDG_RUNTIME_DIR", "/var/tmp/.cache")
         assert get_runtime_dir(create=False) == os.path.join("/var/tmp/.cache", "borg")