Error: Definition of nested anonymous union in packed must be __packed

I'm using the ARM DS-5 with the ARM 5 Compiler Toolchain. I'm attempting to use the "mavlink_types.h" (link: github.com/.../c_library_v1). However, I've got an error said that: Definition of nested anonymous union in packed "param_union" must be __packed. Does anyone know how to fix this ??