Docker: adding a file from a parent directory

In my Dockerfile I’ve got :

ADD ../../myapp.war /opt/tomcat7/webapps/

That file exists as ls ../../myapp.war returns me the correct file but when I execute sudo docker build -t myapp . I’ve got :

Step 1 : ADD ../../myapp.war /opt/tomcat7/webapps/
2014/07/02 19:18:09 ../../myapp.war: no such file or directory

Does somebody know why and how to do it correctly?