diff --git a/event-schemas/examples/m.room_key b/event-schemas/examples/m.room_key
index 2348e47d..51249199 100644
--- a/event-schemas/examples/m.room_key
+++ b/event-schemas/examples/m.room_key
@@ -3,7 +3,7 @@
     "algorithm": "m.megolm.v1.aes-sha2",
     "room_id": "!UCnwUWwIKhcpaPTHtR:sw1v.org",
     "session_id": "X3lUlvLELLYxeTx4yOVu6UDpasGEVO0Jbu+QFnm0cKQ",
-    "session_key": "AgAAAADxKHa9uFxcXzwYoNueL5Xqi69IkD4sni8LlfJL7qNBEYbf8q5V1G7D/0GHj81JbEFsaE8JOHXJCyIqUGU9svVEi52SAGiC4lpID43TAeGfYc64rUsBx5ovhZl8WrdszLxld29I+7H9e8GZt/NVd/ZQEBBfOv3vrgoODT3WpJiWZ7VEIjL6gspKkkRTDcmwYU6Eff+A11iJ2tEC9njtCeNfTrK7XUIPoXkHWmEjPwqdSQi9pqVb1OYRKT7un7WFJzo0WEw8xjo6wyEolSikaBr3/o8FhoIMIA9KvbjR4y1WDg"
+    "session_key": "AgAAAADxKHa9uFxcXzwYoNueL5Xqi69IkD4sni8LlfJL7qNBEY..."
   },
   "type": "m.room_key"
 }
diff --git a/event-schemas/schema/m.room_key b/event-schemas/schema/m.room_key
index f5e4ac29..ef8c51c0 100644
--- a/event-schemas/schema/m.room_key
+++ b/event-schemas/schema/m.room_key
@@ -4,18 +4,29 @@ allOf:
 
 description: |-
   This event type is used to exchange keys for end-to-end encryption. Typically
-  it is encrypted as an ``m.room.encrypted`` event.
+  it is encrypted as an ``m.room.encrypted`` event, then sent as a `to-device`_ event.
 properties:
   content:
     properties:
       algorithm:
         type: string
+        enum: ["m.megolm.v1.aes-sha2"]
         description: |-
-          The encryption algorithm the keys in this event are to be used
-          with. The value of this field determines which other properties will
-          be present.
+          The encryption algorithm the key in this event is to be used with.
+      room_id:
+        type: string
+        description: The room where the key is used.
+      session_id:
+        type: string
+        description: The ID of the session that the key is for.
+      session_key:
+        type: string
+        description: The key to be exchanged.
     required:
       - algorithm
+      - room_id
+      - session_id
+      - session_key
     type: object
   type:
     enum: