I'm experimenting with underlays, but the catkin plugin is pulling the deb for the package despite it being present in the underlay. From stepping through snapcraft with pdb, it appears that the issue is that the script that _Catkin.find runs always fails, which the plugin interprets as the package not found in the underlay. When I changed https://github.com/snapcore/snapcraft/blob/9e8e336deb406cbecdda11e5ca7a25c329454e98/snapcraft/plugins/catkin.py#L911 to: subprocess.check_output(['/bin/bash', f.name, 'catkin_find'] + arguments).decode('utf8').strip() The stderr showed the following: Traceback (most recent call last): File "/home/ruddick/Desktop/ros_underlay/parts/my-msgs/catkin/install/opt/ros/kinetic/bin/catkin_find", line 11, in <module> from catkin.find_in_workspaces import find_in_workspaces ImportError: No module named catkin.find_in_workspaces It looks like /home/ruddick/Desktop/ros_underlay/parts/my-msgs/catkin/install/opt/ros/kinetic/lib/python2.7/dist-packages needs to be added to the PYTHONPATH in the temp script (currently it's only /home/ruddick/Desktop/ros_underlay/parts/my-msgs/catkin/install/usr/lib/python2.7/dist-packages)