diff --git a/repos/os/src/test/timer/main.cc b/repos/os/src/test/timer/main.cc
index d830253cad..702844b04a 100644
--- a/repos/os/src/test/timer/main.cc
+++ b/repos/os/src/test/timer/main.cc
@@ -79,7 +79,7 @@ struct Stress_test
 		enum { DURATION_US         = DURATION_SEC * 1000 * 1000 };
 		enum { MIN_TIMER_PERIOD_US = 1000 };
 		enum { MAX_CNT_BASE        = DURATION_US / MIN_TIMER_PERIOD_US };
-		enum { MAX_CNT_TOLERANCE   = MAX_CNT_BASE / 10 };
+		enum { MAX_CNT_TOLERANCE   = MAX_CNT_BASE / 9 };
 		enum { MAX_CNT             = MAX_CNT_BASE + MAX_CNT_TOLERANCE };
 		enum { MIN_CNT             = DURATION_US / MAX_SLV_PERIOD_US / 2 };