diff --git a/tests/conftest.py b/tests/conftest.py
index b9d0f6f8..229620e7 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,8 +1,16 @@
 # Collects FeatureScript tests (`*_test.fs`), run with the evaluator in fs_eval
 import pathlib
 
+import pytest
+
 from fs_eval.pytest_plugin import pytest_collect_file  # noqa: F401
 
+
+@pytest.fixture(autouse=True)
+def _no_branch_override(monkeypatch):
+    """The Onshape workflow sets FS_BRANCH for fs, which would put every test on its branch."""
+    monkeypatch.delenv("FS_BRANCH", raising=False)
+
 # Tests write files as they're written on Linux and macOS, with "\n" line endings. On Windows, text written without
 # newline="" gets "\r\n", which fs keeps (it syncs files byte for byte), so every test's fixtures would differ.
 _write_text = pathlib.Path.write_text