docker build with --build-arg with multiple arguments

According to the documentation, it's possible to define multiple args for the flag --build-arg, but I can't find out how. I tried the following:

docker build -t essearch/ess-elasticsearch:1.7.6 --build-arg number_of_shards=5 number_of_replicas=2 --no-cache .

=> This returns an error.

I also tried:

docker build -t essearch/ess-elasticsearch:1.7.6 --build-arg number_of_shards=5,number_of_replicas=2 --no-cache .

=> This sets one variable, number_of_shards, to the value "5,number_of_replicas=2"

Any idea how I can define multiple arguments?