Using the percent sign in TeamCity build scripts

I am trying to set up a TeamCity build process that runs a custom command line script. The script uses a variable so it needs a percent sign (e.g. %x). But TeamCity uses percent signs for its properties (e.g. %build.number%), so the percent sign in the script gets removed when it runs.

If the script contains this:

for /d %x in ("c:\*") do @echo "%x"

This is what it actually runs:

for /d x in ("\*") do @echo "x"

How can I write my script so it can include variables?