One quick strategy, until packages get updated to 0.19, you can also create a vendor folder, add it to the source-directories and copy into it the source code for some of the packages you depend on. Sometimes, the source code needs no modification at all or it can be automatically handled by elm-upgrade. Once the package has been updated for 0.19 you can delete the module from vendor and re-add it to your dependencies, eventually getting rid of the vendor folder.