diff --git a/docs/changelog.rst b/docs/changelog.rst
index 376ec06..4444add 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -1,6 +1,10 @@
 Changelog
 =========
 
+v3.5.1 (2022-02-16)
+-------------------
+- Use ``time.monotonic`` instead of ``time.time`` for calculating timeouts.
+
 v3.5.0 (2022-02-15)
 -------------------
 - Enable use as context decorator
diff --git a/src/filelock/_api.py b/src/filelock/_api.py
index d3cffc4..282106f 100644
--- a/src/filelock/_api.py
+++ b/src/filelock/_api.py
@@ -161,7 +161,7 @@ def acquire(
 
         lock_id = id(self)
         lock_filename = self._lock_file
-        start_time = time.time()
+        start_time = time.monotonic()
         try:
             while True:
                 with self._thread_lock:
@@ -172,7 +172,7 @@ def acquire(
                 if self.is_locked:
                     _LOGGER.debug("Lock %s acquired on %s", lock_id, lock_filename)
                     break
-                elif 0 <= timeout < time.time() - start_time:
+                elif 0 <= timeout < time.monotonic() - start_time:
                     _LOGGER.debug("Timeout on acquiring lock %s on %s", lock_id, lock_filename)
                     raise Timeout(self._lock_file)
                 else: