diff --git a/changelogs/client_server/newsfragments/1478.clarification b/changelogs/client_server/newsfragments/1478.clarification
new file mode 100644
index 00000000..df90d278
--- /dev/null
+++ b/changelogs/client_server/newsfragments/1478.clarification
@@ -0,0 +1 @@
+Further clarify that `state_default` on `m.room.power_levels` is 0 when no power levels event is in the room.
\ No newline at end of file
diff --git a/data/event-schemas/schema/m.room.power_levels.yaml b/data/event-schemas/schema/m.room.power_levels.yaml
index a24b2e44..c3ea94aa 100644
--- a/data/event-schemas/schema/m.room.power_levels.yaml
+++ b/data/event-schemas/schema/m.room.power_levels.yaml
@@ -75,6 +75,9 @@ properties:
         description: |-
             The default level required to send state events. Can be overridden
             by the `events` key. Defaults to 50 if unspecified.
+
+            **Note**: When there is no `m.room.power_levels` event in the room, this defaults
+            to 0. See description for more information.
         type: integer
       users:
         additionalProperties: