diff --git a/repos/os/src/test/timer/main.cc b/repos/os/src/test/timer/main.cc
index 899c78a56a..504755a2f0 100644
--- a/repos/os/src/test/timer/main.cc
+++ b/repos/os/src/test/timer/main.cc
@@ -147,8 +147,10 @@ int main(int argc, char **argv)
 			i += s.num();
 		}
 		elapsed_ms = main_timer.elapsed_ms() - elapsed_ms;
-		unsigned const min_ms = ((i - 1) * period_us) / 1000;
-		unsigned const max_ms = (i * period_us) / 1000;
+		unsigned const min_ms     = ((i - 1) * period_us) / 1000;
+		unsigned const max_us     = i * period_us;
+		unsigned const max_err_us = max_us / 100;
+		unsigned const max_ms     = (max_us + max_err_us) / 1000;
 		if (min_ms > elapsed_ms || max_ms < elapsed_ms) {
 			PERR("Timing %u ms period %u times failed: %u ms (min %u, max %u)",
 			     period_us / 1000, i, elapsed_ms, min_ms, max_ms);