diff --git a/osu.Game/Online/RealtimeMultiplayer/InvalidStateException.cs b/osu.Game/Online/RealtimeMultiplayer/InvalidStateException.cs
new file mode 100644
index 0000000000..8393e7e925
--- /dev/null
+++ b/osu.Game/Online/RealtimeMultiplayer/InvalidStateException.cs
@@ -0,0 +1,15 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+
+namespace osu.Game.Online.RealtimeMultiplayer
+{
+    public class InvalidStateException : Exception
+    {
+        public InvalidStateException(string message)
+            : base(message)
+        {
+        }
+    }
+}
diff --git a/osu.Game/Online/RealtimeMultiplayer/NotJoinedRoomException.cs b/osu.Game/Online/RealtimeMultiplayer/NotJoinedRoomException.cs
new file mode 100644
index 0000000000..1b264d1ac5
--- /dev/null
+++ b/osu.Game/Online/RealtimeMultiplayer/NotJoinedRoomException.cs
@@ -0,0 +1,12 @@
+using System;
+
+namespace osu.Game.Online.RealtimeMultiplayer
+{
+    public class NotJoinedRoomException : Exception
+    {
+        public NotJoinedRoomException()
+            : base("This user has not yet joined a multiplayer room.")
+        {
+        }
+    }
+}
\ No newline at end of file
diff --git a/osu.Game/Online/RealtimeMultiplayer/UserAlreadyInMultiplayerRoom.cs b/osu.Game/Online/RealtimeMultiplayer/UserAlreadyInMultiplayerRoom.cs
new file mode 100644
index 0000000000..9a2090c710
--- /dev/null
+++ b/osu.Game/Online/RealtimeMultiplayer/UserAlreadyInMultiplayerRoom.cs
@@ -0,0 +1,15 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+
+namespace osu.Game.Online.RealtimeMultiplayer
+{
+    public class UserAlreadyInMultiplayerRoom : Exception
+    {
+        public UserAlreadyInMultiplayerRoom()
+            : base("This user is already in a room.")
+        {
+        }
+    }
+}