Index: lnt/tests/test_suite.py
===================================================================
--- lnt/tests/test_suite.py
+++ lnt/tests/test_suite.py
@@ -482,6 +482,9 @@
             if 'TEST_SUITE_RUN_TYPE' not in defs:
                 defs['TEST_SUITE_RUN_TYPE'] = 'ref'
 
+        if self.opts.only_test:
+            defs['BENCH_DIRS'] = self.opts.only_test[0]
+
         for item in tuple(self.opts.cmake_defines) + tuple(extra_cmake_defs):
             k, v = item.split('=', 1)
             # make sure the overriding of the settings above also works