diff --git a/INSTALL b/INSTALL
index 51c0e79..29052eb 100644
--- a/INSTALL
+++ b/INSTALL
@@ -14,9 +14,12 @@ Dependencies
 * Python for the filters
 * 'testtools' (On Debian and Ubuntu systems the 'python-testtools' package,
   the testtools package on pypi, or https://launchpad.net/testtools) for
-  the extended test API which permits attachments. Version 0.9.30 or newer is 
+  the extended test API which permits attachments. Version 0.9.30 or newer is
   required. Of particular note, http://testtools.python-hosting.com/ is not
   the testtools you want.
+* 'testscenarios' (On Debian and Ubuntu systems the 'python-testscenarios'
+  package, the 'testscenarios' package on pypi, or
+  https://launchpad.net/testscenarios) for running some of the python unit tests.
 * A C compiler for the C bindings
 * Perl for the Perl tools (including subunit-diff)
 * Check to run the subunit test suite.