EDIT: The problems reported here and in #16443 turned out to be due to using the property incorrectly. The documentation of the `NO_SYSTEM_FROM_IMPORTED` does not clearly state that it is meant to be set on the *consumers* of imported targets. The original report follows. --- Since #16443 was fixed, it used to be possible to `set_target_properties(<target> PROPERTIES NO_SYSTEM_FROM_IMPORTED true)` on an IMPORTED target. However, this seems to not be actually working anymore (tried with cmake 3.8 and 3.9). When building the following `main.cpp` with the `CMakeLists.txt` below, one can see the build command uses `-isystem` instead of `-I` for boost: `main.cpp`: ``` #include <boost/optional.hpp> int main(int argc, char** argv) { boost::optional<int> opt; return 0; } ``` `CMakeLists.txt`: ``` cmake_minimum_required(VERSION 3.9) project(no-system-from-imported) find_package(Boost 1.62 REQUIRED) set_target_properties(Boost::boost PROPERTIES NO_SYSTEM_FROM_IMPORTED true) add_executable(main main.cpp) target_link_libraries(main Boost::boost) ``` Build command: ``` cmake -DBOOST_ROOT=/tmp/boost_1_64_0_src /tmp/no_system_from_imported` VERBOSE=1 make ``` Outputs (notice `-isystem` instead of `-I`: ``` ... /usr/lib64/ccache/c++ -isystem /tmp/boost_1_64_0_src -o CMakeFiles/main.dir/main.cpp.o -c /tmp/no_system_from_imported/main.cpp ... ```