diff --git a/data/event-schemas/schema/m.space.child.yaml b/data/event-schemas/schema/m.space.child.yaml
index a2ff3763..c73d440f 100644
--- a/data/event-schemas/schema/m.space.child.yaml
+++ b/data/event-schemas/schema/m.space.child.yaml
@@ -9,6 +9,8 @@ properties:
         type: array
         description: |-
           A list of servers to try and join through. See also: [Routing](/appendices/#routing).
+
+          When not present or invalid, the child room is not considered to be part of the space.
         items:
           type: string
       order:
diff --git a/data/event-schemas/schema/m.space.parent.yaml b/data/event-schemas/schema/m.space.parent.yaml
index b1864f96..fb633789 100644
--- a/data/event-schemas/schema/m.space.parent.yaml
+++ b/data/event-schemas/schema/m.space.parent.yaml
@@ -9,6 +9,8 @@ properties:
         type: array
         description: |-
           A list of servers to try and join through. See also: [Routing](/appendices/#routing).
+
+          When not present or invalid, the room is not considered to be part of the parent space.
         items:
           type: string
       canonical: