.asm Compile error

when i try to do make all in the main makefile, it comes up with an error which says

 Building Kernel
 make -C ./kernel
 make[1]: Entering directory '/home/mainuser/Documents/9/devos-master/kernel'
 nasm   -f elf -o  -c arch/x86/start.asm -o  arch/x86/start.o
 arch/x86/start.asm: fatal: more than one output file specified: arch/x86/start.o

 make[1]: *** [Makefile:64: arch/x86/start.o] Error 1
 make[1]: Leaving directory '/home/mainuser/Documents/9/devos-master/kernel'
 make: *** [Makefile:14: all] Error 2