diff --git a/mempalace/palace.py b/mempalace/palace.py
index 917c76d..07efb6a 100644
--- a/mempalace/palace.py
+++ b/mempalace/palace.py
@@ -329,14 +329,21 @@ def mine_palace_lock(palace_path: str):
     *different* palaces can still run in parallel — we only serialize
     writes into the same palace, which is the correctness boundary.
 
+    The key is derived from a fully normalized form of the path:
+    `realpath` resolves symlinks and `..` segments, and `normcase` folds
+    case on Windows (which has a case-insensitive filesystem). Without
+    normcase, `C:\\Palace` and `c:\\palace` would hash to different keys
+    on Windows and let two concurrent mines touch the same on-disk palace.
+
     Non-blocking: if another `mine` is already writing to this palace,
     raise MineAlreadyRunning so the caller can exit cleanly instead of
     piling up as a waiting worker.
     """
     lock_dir = os.path.join(os.path.expanduser("~"), ".mempalace", "locks")
     os.makedirs(lock_dir, exist_ok=True)
-    resolved = os.path.abspath(os.path.expanduser(palace_path))
-    palace_key = hashlib.sha256(resolved.encode()).hexdigest()[:16]
+    resolved = os.path.realpath(os.path.expanduser(palace_path))
+    lock_key_source = os.path.normcase(resolved)
+    palace_key = hashlib.sha256(lock_key_source.encode()).hexdigest()[:16]
     lock_path = os.path.join(lock_dir, f"mine_palace_{palace_key}.lock")
 
     lf = open(lock_path, "w")
diff --git a/tests/test_palace_locks.py b/tests/test_palace_locks.py
index a7596b9..601c894 100644
--- a/tests/test_palace_locks.py
+++ b/tests/test_palace_locks.py
@@ -22,6 +22,18 @@ from mempalace.palace import (
 )
 
 
+def _get_mp_context():
+    """Pick a start method that works on every CI runner.
+
+    `fork` is cheaper (no re-import) but is unavailable on Windows, so we fall
+    back to `spawn` there. `spawn` inherits ``os.environ`` (including the
+    monkeypatched ``HOME``) and re-imports the ``mempalace`` package in the
+    child, which is sufficient for the lock-file semantics exercised here.
+    """
+    start_method = "spawn" if os.name == "nt" else "fork"
+    return multiprocessing.get_context(start_method)
+
+
 # ---------------------------------------------------------------------------
 # Helpers
 # ---------------------------------------------------------------------------
@@ -75,7 +87,7 @@ def test_same_palace_serializes_across_processes(tmp_path, monkeypatch):
     ready = str(tmp_path / "ready")
     release = str(tmp_path / "release")
 
-    ctx = multiprocessing.get_context("fork")
+    ctx = _get_mp_context()
     holder = ctx.Process(target=_hold_lock, args=(palace, ready, release))
     holder.start()
     try:
@@ -104,7 +116,7 @@ def test_different_palaces_dont_conflict(tmp_path, monkeypatch):
     ready = str(tmp_path / "ready_a")
     release = str(tmp_path / "release_a")
 
-    ctx = multiprocessing.get_context("fork")
+    ctx = _get_mp_context()
     holder = ctx.Process(target=_hold_lock, args=(palace_a, ready, release))
     holder.start()
     try: