diff --git a/src/xai_sdk/poll_timer.py b/src/xai_sdk/poll_timer.py
index 9e71c76..b36ed70 100644
--- a/src/xai_sdk/poll_timer.py
+++ b/src/xai_sdk/poll_timer.py
@@ -24,7 +24,11 @@ def __init__(
             context: A description of what is being waited on (e.g. "waiting for document to be indexed").
                 Included in the TimeoutError message for easier debugging.
         """
-        self._start = time.time()
+        # A monotonic clock is required for duration accounting: time.time()
+        # is a wall clock, so NTP corrections, manual clock changes or VM
+        # suspend/restore can make a healthy poll time out immediately (or
+        # poll far beyond the caller's timeout).
+        self._start = time.monotonic()
         self._timeout = timeout or datetime.timedelta(minutes=10)
         self._interval = interval or datetime.timedelta(seconds=1)
         self._context = context
@@ -38,7 +42,7 @@ def sleep_interval_or_raise(self) -> float:
         Raises:
             TimeoutError when the total polling time is used up.
         """
-        runtime = time.time() - self._start
+        runtime = time.monotonic() - self._start
         if runtime > self._timeout.total_seconds():
             message = f"Polling timed out after {runtime:.1f}s"
             if self._context:
diff --git a/tests/poll_timer_test.py b/tests/poll_timer_test.py
new file mode 100644
index 0000000..aeb3f76
--- /dev/null
+++ b/tests/poll_timer_test.py
@@ -0,0 +1,55 @@
+"""PollTimer must account elapsed time on a monotonic clock.
+
+time.time() is a wall clock: NTP corrections, manual clock changes or VM
+suspend/restore can move it, making a healthy poll time out immediately
+(a forward adjustment) or poll far beyond the caller's timeout (a
+backward adjustment). Regression for #203.
+"""
+
+import datetime
+from unittest.mock import patch
+
+from xai_sdk.poll_timer import PollTimer
+
+
+def test_forward_wall_clock_adjustment_does_not_time_out():
+    # The wall clock jumps forward 9900s between construction and the first
+    # sleep computation; monotonic elapsed time is still ~0.5s.
+    with patch("xai_sdk.poll_timer.time.monotonic", side_effect=[100.0, 100.5]):
+        timer = PollTimer(
+            timeout=datetime.timedelta(seconds=10),
+            interval=datetime.timedelta(seconds=20),
+        )
+        interval = timer.sleep_interval_or_raise()
+
+    assert interval == 9.5
+
+
+def test_backward_wall_clock_adjustment_does_not_extend_timeout():
+    # The wall clock jumps backward while 15s actually elapse: the poll must
+    # still time out instead of quietly polling beyond the caller's timeout.
+    with patch("xai_sdk.poll_timer.time.monotonic", side_effect=[10_000.0, 10_015.0]):
+        timer = PollTimer(
+            timeout=datetime.timedelta(seconds=10),
+            interval=datetime.timedelta(seconds=1),
+        )
+        try:
+            timer.sleep_interval_or_raise()
+        except TimeoutError as e:
+            assert "timed out after 15.0s" in str(e)
+        else:
+            raise AssertionError("expected TimeoutError")
+
+
+def test_timeout_still_raises_on_real_elapsed_time():
+    with patch("xai_sdk.poll_timer.time.monotonic", side_effect=[100.0, 200.0]):
+        timer = PollTimer(
+            timeout=datetime.timedelta(seconds=10),
+            interval=datetime.timedelta(seconds=1),
+        )
+        try:
+            timer.sleep_interval_or_raise()
+        except TimeoutError as e:
+            assert "timed out after 100.0s" in str(e)
+        else:
+            raise AssertionError("expected TimeoutError")