Note that the problem does not occur with Dosbox 0.74. I'm guessing it does not emulate the fpu at all. Dosbox 0.74 seems to always have an FPU. I wasn't able to configure it so that this simple test program doesn't detect an FPU: ; nasm fpu_test.asm -o fpu_test.com cpu 8086 org 100h start: mov dx, …