CMake Error: WEBP_LIBRARIES NOTFOUND

When building aesprite on Windows I receive the following error:

-- Configuring done
CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
WEBP_LIBRARIES
    linked by target "app-lib" in directory .../aseprite/src/app

The error seems to stem from this line in CMakeLists.txt:

I have downloaded skia, but do I need to build it in order for the WEBP_LIBRARIES variable to be set?