diff --git a/metronomes/metronome.py b/metronomes/metronome.py
index 975f99d..b6703b4 100644
--- a/metronomes/metronome.py
+++ b/metronomes/metronome.py
@@ -5,6 +5,7 @@
 import escape
 from emptylog import EmptyLogger, LoggerProtocol
 from cantok import AbstractToken, SimpleToken
+from locklib import ContextLockProtocol
 
 from metronomes.errors import RunStoppedMetronomeError, RunAlreadyStartedMetronomeError, StopNotStartedMetronomeError, StopStoppedMetronomeError
 
@@ -14,15 +15,15 @@ def __init__(self, duration: Union[int, float], callback: Callable[[], Any], sup
         if duration <= 0:
             raise ValueError('The duration of the metronome iteration (tick-tock time) must be greater than zero.')
 
-        self.duration = duration
-        self.callback = callback
-        self.suppress_exceptions = suppress_exceptions
-        self.logger = logger
-        self.token = SimpleToken(cancellation_token) if cancellation_token is not None else SimpleToken()
-        self.thread = None
-        self.started = False
-        self.stopped = False
-        self.lock = Lock()
+        self.duration: Union[int, float] = duration
+        self.callback: Callable[[], Any] = callback
+        self.suppress_exceptions: bool = suppress_exceptions
+        self.logger: LoggerProtocol = logger
+        self.token: AbstractToken = SimpleToken(cancellation_token) if cancellation_token is not None else SimpleToken()
+        self.thread: Optional[Thread] = None
+        self.started: bool = False
+        self.stopped: bool = False
+        self.lock: ContextLockProtocol = Lock()
 
     def start(self) -> None:
         with self.lock:
diff --git a/pyproject.toml b/pyproject.toml
index 1ff677f..4432625 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -15,6 +15,7 @@ dependencies = [
     'emptylog>=0.0.4',
     'cantok>=0.0.22',
     'escaping>=0.0.11',
+    'locklib>=0.0.14',
 ]
 classifiers = [
     'Operating System :: OS Independent',