diff --git a/doc/rados/operations/pg-states.rst b/doc/rados/operations/pg-states.rst
index eb0e298e288..8ba92ac0267 100644
--- a/doc/rados/operations/pg-states.rst
+++ b/doc/rados/operations/pg-states.rst
@@ -70,3 +70,7 @@ map is ``active + clean``.
 *Remapped*
   The placement group is temporarily mapped to a different set of OSDs from what
   CRUSH specified.
+
+*Undersized*
+  The placement group fewer copies than the configured pool replication level.
+