When running make -d in build I notice that Make first checks ../src/lib.c as expected but then also checks ../../src/lib.c which doesn't exist, and this apparently triggers a rebuild of src/CMakeFiles/lib.dir/lib.c.o . ../../src/lib.c comes from src/CMakeFiles/lib.dir/compiler_depend.make . With the CCACHE_BASEDIR line commented out in repro there is no such entry (not even one with an absolute path) in compiler_depend.make . I haven't investigated this further, but I suspect that it is a consequence of ccache rewriting absolute paths on the command line to relative, thus implicitly rewriting absolute paths to relative in src/CMakeFiles/lib.dir/lib.c.o.d .

I guess CMake isn't really at fault here, but I thought that I should report the issue here anyway since more people may stumble on this. Maybe there is an easy enough fix?