conan: Can't use cmake generator "NMake Makefiles" with conan

If I set environment variable CONAN_CMAKE_GENERATOR to"NMake Makefiles", conan correctly passes -G "NMake Makefiles" to cmake during configure but build fails with

NMAKE : fatal error U1065: invalid option 'j'                                                     
Stop.                                                                                             
ERROR: PROJECT: Error in build() method, line 30                                                  
        cmake.build()                                                                             
        ConanException: Error 2 while executing cmake --build C:\Work\conan-test\build -- -j4

the problem is here: https://github.com/conan-io/conan/blob/develop/conans/client/build/cmake.py

            if "Makefiles" in self.generator:
                if "--" not in args:
                    args.append("--")
                args.append("-j%i" % cpu_count())

You always add -j flag for Makefiles generators but NMake does not understand that.