diff --git a/tests/test_mods.py b/tests/test_mods.py
index 3a656d9..fc76fec 100644
--- a/tests/test_mods.py
+++ b/tests/test_mods.py
@@ -36,6 +36,7 @@ def zip_bytes(files, links=()):
     return buf.getvalue()
 
 
+@unittest.skipIf(sys.platform == "win32", "the helper runs on the Frame (Linux): /proc, flock and POSIX prefix paths")
 class FakeLibrary(unittest.TestCase):
     """A Steam library with Gravitas's real layout, and pinned downloads served from memory."""
 
@@ -230,9 +231,10 @@ class Downloads(FakeLibrary):
 
 class Actions(FakeLibrary):
     def test_one_change_at_a_time(self):
+        import fcntl
         lock = Path(tempfile.mkdtemp()) / "mods.lock"
         with mock.patch.object(frame_mods, "LOCK", lock), open(lock, "w") as held:
-            frame_mods.fcntl.flock(held, frame_mods.fcntl.LOCK_EX)
+            fcntl.flock(held, fcntl.LOCK_EX)
             with self.assertRaisesRegex(frame_mods.Fail, "another mod action"):
                 frame_mods.main(["install", str(APPID)])
             self.assertFalse(frame_mods.status(APPID)["installed"])
@@ -294,6 +296,7 @@ class Start(FakeLibrary):
 
 
 class Helper(unittest.TestCase):
+    @unittest.skipIf(sys.platform == "win32", "uninstall takes the flock lock, which only exists on the Frame (Linux)")
     def test_unexpected_errors_are_still_json(self):
         # A receipt from another version, without "exe": a KeyError, not a traceback.
         script = (ROOT / "ui" / "frame_mods.py").read_text().replace(
diff --git a/ui/frame_mods.py b/ui/frame_mods.py
index 482b2ea..4f42f6f 100644
--- a/ui/frame_mods.py
+++ b/ui/frame_mods.py
@@ -22,7 +22,6 @@ from python.org, each checked against a pinned hash. Files live in
 <prefix>/drive_c/frame-control, never in the game's own folder, and a receipt
 records what to remove.
 """
-import fcntl
 import hashlib
 import json
 import os
@@ -511,6 +510,7 @@ def main(argv):
     action = {"status": status, "install": install, "start": start, "uninstall": uninstall}[argv[0]]
     if action is status:
         return status(int(argv[1]))
+    import fcntl  # only on the Frame; the server and its tests also import this module on Windows
     # One change at a time, or an uninstall could delete what an install is moving in.
     LOCK.parent.mkdir(parents=True, exist_ok=True)
     with open(LOCK, "w") as lock: