diff --git a/test/rt/testthd.c b/test/rt/testthd.c
index 5d7e18eff..0f0c88c86 100644
--- a/test/rt/testthd.c
+++ b/test/rt/testthd.c
@@ -196,28 +196,28 @@ static void thd4_execute(void) {
   chThdSleepMicroseconds(100000);
   test_assert_time_window(1,
                           time + US2ST(100000),
-                          time + US2ST(100000) + CH_CFG_ST_TIMEDELTA);
+                          time + US2ST(100000) + CH_CFG_ST_TIMEDELTA + 1);
 
   /* Timeouts in milliseconds.*/
   time = chVTGetSystemTime();
   chThdSleepMilliseconds(100);
   test_assert_time_window(2,
                           time + MS2ST(100),
-                          time + MS2ST(100) + CH_CFG_ST_TIMEDELTA);
+                          time + MS2ST(100) + CH_CFG_ST_TIMEDELTA + 1);
 
   /* Timeouts in seconds.*/
   time = chVTGetSystemTime();
   chThdSleepSeconds(1);
   test_assert_time_window(3,
                           time + S2ST(1),
-                          time + S2ST(1) + CH_CFG_ST_TIMEDELTA);
+                          time + S2ST(1) + CH_CFG_ST_TIMEDELTA + 1);
 
   /* Absolute timelines.*/
   time = chVTGetSystemTime() + MS2ST(100);
   chThdSleepUntil(time);
   test_assert_time_window(4,
                           time,
-                          time + CH_CFG_ST_TIMEDELTA);
+                          time + CH_CFG_ST_TIMEDELTA + 1);
 }
 
 ROMCONST struct testcase testthd4 = {