diff --git a/zircon/docs/syscalls/clock_get_monotonic.md b/zircon/docs/syscalls/clock_get_monotonic.md
index b2fba2e51f3822e8dd27d96df5f716d2a8ee8069..912b8892371308b44711327ac95142abfd7b1d85 100644
--- a/zircon/docs/syscalls/clock_get_monotonic.md
+++ b/zircon/docs/syscalls/clock_get_monotonic.md
@@ -20,7 +20,8 @@ zx_time_t zx_clock_get_monotonic(void);
 
 `zx_clock_get_monotonic()` returns the current time in the system
 monotonic clock. This is the number of nanoseconds since the system was
-powered on.
+powered on. It does not always reset on reboot and does not adjust during
+sleep, and thus should not be used as a reliable source of uptime.
 
 ## RIGHTS