diff --git a/tangostationcontrol/test/beam/test_delays.py b/tangostationcontrol/test/beam/test_delays.py
index 4169f4d53b76d429a5a9efc03d4a7403dcae1e4b..5e67e47d877a502d9a80ff52f44111164335aba7 100644
--- a/tangostationcontrol/test/beam/test_delays.py
+++ b/tangostationcontrol/test/beam/test_delays.py
@@ -12,7 +12,8 @@ import numpy
 import numpy.testing
 import threading
 
-from tangostationcontrol.beam.delays import Delays, threading as delays_threading
+from tangostationcontrol.beam import delays
+from tangostationcontrol.beam.delays import Delays
 from tangostationcontrol.common.constants import MAX_ANTENNA, N_beamlets_ctrl
 
 from test import base
@@ -252,13 +253,14 @@ class TestDelaysBulk(base.TestCase):
         # most about the worst case for a thread. We assume the worst
         # case thread is slowed down by all the work of the other threads.
         self.assertLess(
-            max(duration_results_ms) / nr_threads, single_thread_execution_time * 1.25
+            max(duration_results_ms) / nr_threads,
+            single_thread_execution_time * 1.50,  # 50% tolerance
         )
 
         # report the performance if we remove the compute lock around casacore, to detect
         # on which systems it matters.
 
-        with mock.patch.object(delays_threading, "Lock") as m_lock:
+        with mock.patch.object(delays, "compute_lock") as m_lock:
             # compare against multi-threaded performance
             duration_results_ms = []
             threads = [