diff --git a/hermes_state.py b/hermes_state.py
index a4d9b9429ac..a2a019a7a98 100644
--- a/hermes_state.py
+++ b/hermes_state.py
@@ -46,6 +46,11 @@ def _compression_lock_holder_process_is_dead(holder: str) -> bool:
     only when the kernel proves that PID no longer exists; legacy/unstructured
     holders and permission errors remain protected until normal TTL expiry.
     """
+    # Python's os.kill(pid, 0) is a non-destructive liveness probe on POSIX.
+    # On Windows, any non-CTRL signal value is implemented with
+    # TerminateProcess, so fall back to TTL-only recovery there.
+    if os.name == "nt":
+        return False
     match = _COMPRESSION_LOCK_HOLDER_PID_RE.search(holder or "")
     if match is None:
         return False
@@ -59,7 +64,7 @@ def _compression_lock_holder_process_is_dead(holder: str) -> bool:
         os.kill(pid, 0)
     except ProcessLookupError:
         return True
-    except (PermissionError, OSError):
+    except (PermissionError, OSError, OverflowError):
         return False
     return False
 
diff --git a/tests/test_hermes_state_compression_locks.py b/tests/test_hermes_state_compression_locks.py
index 2655a75c05d..05aaaeb3ab1 100644
--- a/tests/test_hermes_state_compression_locks.py
+++ b/tests/test_hermes_state_compression_locks.py
@@ -137,12 +137,30 @@ def test_unstructured_holder_waits_for_ttl(
     assert db.try_acquire_compression_lock(
         "sess1", "legacy_holder", ttl_seconds=300
     ) is True
-    kill = monkeypatch.setattr(
+    monkeypatch.setattr(
         hermes_state.os,
         "kill",
         lambda *_args: pytest.fail("unstructured holder must not probe a PID"),
     )
-    assert kill is None
+    assert db.try_acquire_compression_lock(
+        "sess1", "pid=525252:tid=2:agent=def:nonce=other", ttl_seconds=300
+    ) is False
+
+
+def test_windows_uses_ttl_only_without_os_kill(
+    db: SessionDB, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    holder = "pid=424242:tid=1:agent=abc:nonce=windows"
+    assert db.try_acquire_compression_lock(
+        "sess1", holder, ttl_seconds=300
+    ) is True
+    monkeypatch.setattr(hermes_state.os, "name", "nt")
+    monkeypatch.setattr(
+        hermes_state.os,
+        "kill",
+        lambda *_args: pytest.fail("Windows must not use os.kill as a PID probe"),
+    )
+
     assert db.try_acquire_compression_lock(
         "sess1", "pid=525252:tid=2:agent=def:nonce=other", ttl_seconds=300
     ) is False