diff --git a/doc/design-monitoring-agent.rst b/doc/design-monitoring-agent.rst
index 14fff7f45ff0e0e587033ce4b036121dcda7e877..d704beb1acdd47a22c37129e0b517617e72e8b9b 100644
--- a/doc/design-monitoring-agent.rst
+++ b/doc/design-monitoring-agent.rst
@@ -91,6 +91,7 @@ primary for and will contain at least:
 - The instance name
 - The instance UUID (stable on name change)
 - The instance running status (up or down)
+- The uptime, as detected by the hypervisor
 - The timestamp of last known change
 - The timestamp of when the status was last checked (see caching, below)
 - The last known reason for change, if any