CLion highlight "size_t" as unknown type in one header, but not in other one — how to make it treat all headers the same?

I have small plain C project, which contains static library. It has structure typical for library: several header files (API) and several C files (implementation). All header files don't include anyhting, all needed system headers (like stdint.h and others) must be included before these API headers.

Problem is, when I add new header file, CLion doesn't recognize system types (like uint32_t and size_t) in it. But in other headers everything is Ok! And I could not understand difference between two: why one header file is completely Ok and other one in same project, with same structure, is full of errors "Can't resolve type X".