CUDA compiling error

I installed CUDA 9.1 on Fedora 27 Linux, 64-bit. The graphics card is GeForce GTX 560Ti, with drivers version 390.59 - the drivers that came with the toolkit.

I tried to compile the CUDA kernel drivers, but it failed with the following error:

Compiling CUDA kernel …
“/usr/local/cuda/bin/nvcc” -arch=sm_21 --cubin “/usr/share/blender/scripts/addons/cycles/source/kernel/kernels/cuda/kernel.cu” -o “/home/ferdi/.cache/cycles/kernels/cycles_kernel_sm21_12FE04C0ECB5D1A51A966E52F8B51F34.cubin” -m64 --ptxas-options="-v" --use_fast_math -DNVCC -D__KERNEL_CUDA_VERSION__=91 -I"/usr/share/blender/scripts/addons/cycles/source"
nvcc fatal : Value ‘sm_21’ is not defined for option ‘gpu-architecture’
CUDA kernel compilation failed, see console for details.

Could someone please help me solve this problem? I spent a lot of time searching online for a solution. No joy. :(

Thank you for your consideration!