diff --git a/lib/jam_ruby/message_factory.rb b/lib/jam_ruby/message_factory.rb
index 7f5cd30fe..85838c19e 100644
--- a/lib/jam_ruby/message_factory.rb
+++ b/lib/jam_ruby/message_factory.rb
@@ -96,6 +96,10 @@
       return Jampb::ClientMessage.new(:type => ClientMessage::Type::TEST_SESSION_MESSAGE, :route_to => SESSION_TARGET_PREFIX + session_id, :test_session_message => test)
 		end
 
+    def session_invitation(receiver_id, invitation_id)
+      session_invitation = Jampb::SessionInvitation.new(:invitation => invitation_id)
+      return Jampb::ClientMessage.new(:type => ClientMessage::Type::SESSION_INVITATION, :route_to => USER_TARGET_PREFIX + receiver_id, :session_invitation => session_invitation)
+    end
     ############## P2P CLIENT MESSAGES #################
 
     # send a request to do a ping
diff --git a/lib/jam_ruby/models/invitation.rb b/lib/jam_ruby/models/invitation.rb
index e636fd418..239a9b2a2 100644
--- a/lib/jam_ruby/models/invitation.rb
+++ b/lib/jam_ruby/models/invitation.rb
@@ -2,6 +2,7 @@ module JamRuby
   class Invitation < ActiveRecord::Base
 
     FRIENDSHIP_REQUIRED_VALIDATION_ERROR = "You can only invite friends"
+    MEMBERSHIP_REQUIRED_OF_MUSIC_SESSION = "You must be a member of the music session to send invitations on behalf of it"
 
     self.primary_key = 'id'
     belongs_to :sender, :inverse_of => :sent_invitations, :class_name => "JamRuby::User", :foreign_key => "sender_id"
@@ -12,10 +13,16 @@ module JamRuby
     validates :receiver, :presence => true
     validates :music_session, :presence => true
 
-    validate :require_are_friends
+    validate :require_sender_in_music_session, :require_are_friends
 
     private
 
+    def require_sender_in_music_session
+      unless music_session.users.exists? sender
+         errors.add(:music_session, MEMBERSHIP_REQUIRED_OF_MUSIC_SESSION)
+      end
+    end
+
     def require_are_friends
       unless receiver.friends.exists? sender
         errors.add(:receiver, FRIENDSHIP_REQUIRED_VALIDATION_ERROR)