class nn.SpatialFullConvolution has been already assigned a parent class

After installing torch7 (from https://github.com/torch/torch7) and kex, running require 'kex' generates the following error

LuaJIT 2.0.2 -- Copyright (C) 2005-2013 Mike Pall. http://luajit.org/
JIT: ON CMOV SSE2 SSE3 SSE4.1 fold cse dce fwd dse narrow loop abc sink fuse
> require 'kex'
/usr/local/share/torch/lua/torch/init.lua:54: class nn.SpatialFullConvolution has been already assigned a parent class

stack traceback:
    [C]: in function 'newmetatable'
    /usr/local/share/torch/lua/torch/init.lua:54: in function 'class'
    /usr/local/share/torch/lua/kex/SpatialFullConvolution.lua:1: in main chunk
    [C]: in function 'dofile'
    /usr/local/share/torch/lua/torch/init.lua:34: in function 'include'
    /usr/local/share/torch/lua/kex/init.lua:7: in main chunk
    [C]: in function 'require'
    stdin:1: in main chunk
    [C]: at 0x00402490

This is a blocking issue. Any idea of what is causing it ? and how to fix it ?

koraykv / kex

class nn.SpatialFullConvolution has been already assigned a parent class #3