Lenya 2.0.3 build fails: Cannot run program "patch" in kupu module (Java 1.6.0.15 on Ubuntu 9.10)

Lenya newbie here. Trying to build Lenya, but failing:

...
custombuild-module-org.apache.lenya.modules.kupu:
Invoking custom build process for module 'org.apache.lenya.modules.kupu'

BUILD FAILED
/home/psulonen/lenya-src/apache-lenya-2.0.3-src/src/targets/webapp-build.xml:174:
The following error occurred while executing this line:
/home/psulonen/lenya-src/apache-lenya-2.0.3-src/src/targets/modules-build.xml:74:
The following error occurred while executing this line:
/home/psulonen/lenya-src/apache-lenya-2.0.3-src/build/lenya/temp/modules-build.xml:125:
The following error occurred while executing this line:
/home/psulonen/lenya-src/apache-lenya-2.0.3-src/src/modules/kupu/build.xml:21:
java.io.IOException: Cannot run program "patch" (in directory
"/home/psulonen/lenya-src/apache-lenya-2.0.3-src/src/modules/kupu"):
java.io.IOException: error=2, No such file or directory

I checked kupu/build.xml, and it references a patch file that also
appears to exist. I verified the MD5 checksum for the archive.
Environment as in title. Using the default build properties.

Help?

Thanks a bundle in advance,

/Petteri