diff --git a/src/Internal/Room.elm b/src/Internal/Room.elm
index 6d13c07..32ad1c5 100644
--- a/src/Internal/Room.elm
+++ b/src/Internal/Room.elm
@@ -92,6 +92,15 @@ accountData key =
     withoutCredentials >> Internal.accountData key
 
 
+{-| Add account data to the room.
+-}
+addAccountData : String -> E.Value -> Room -> Room
+addAccountData eventType content (Room { room, context }) =
+    room
+        |> Internal.addAccountData eventType content
+        |> withCredentials context
+
+
 {-| Adds an internal event to the `Room`. An internal event is a custom event
 that has been generated by the client.
 -}
diff --git a/src/Internal/Values/Room.elm b/src/Internal/Values/Room.elm
index 260bb50..024639d 100644
--- a/src/Internal/Values/Room.elm
+++ b/src/Internal/Values/Room.elm
@@ -28,6 +28,13 @@ accountData key (IRoom room) =
     Dict.get key room.accountData
 
 
+{-| Add new account data to the room.
+-}
+addAccountData : String -> E.Value -> IRoom -> IRoom
+addAccountData eventType content (IRoom room) =
+    IRoom { room | accountData = Dict.insert eventType content room.accountData }
+
+
 {-| Add the data of a single event to the hashdict of events.
 -}
 addEvent : IEvent -> IRoom -> IRoom
diff --git a/src/Internal/Vault.elm b/src/Internal/Vault.elm
index fa5041d..0067cc6 100644
--- a/src/Internal/Vault.elm
+++ b/src/Internal/Vault.elm
@@ -122,7 +122,21 @@ updateWith vaultUpdate ((Vault ({ cred, context } as data)) as vault) =
 
         -- TODO
         AccountDataSet input () ->
-            vault
+            case input.roomId of
+                Just rId ->
+                    case getRoomById rId vault of
+                        Just room ->
+                            room
+                                |> Room.addAccountData input.eventType input.content
+                                |> insertRoom
+                                |> (|>) vault
+
+                        Nothing ->
+                            vault
+
+                -- TODO: Add global account data
+                Nothing ->
+                    vault
 
         -- TODO
         BanUser input () ->