diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
index 5db2088843..394d62a85e 100755
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -163,6 +163,7 @@ def main():
     parser.add_argument('--force', '-f', action='store_true', help='run tests even on platforms where they are disabled by default (e.g. windows).')
     parser.add_argument('--help', '-h', '-?', action='store_true', help='print help text and exit')
     parser.add_argument('--jobs', '-j', type=int, default=4, help='how many test scripts to run in parallel. Default=4.')
+    parser.add_argument('--keepcache', '-k', action='store_true', help='the default behavior is to flush the cache directory on startup. --keepcache retains the cache from the previous testrun.')
     parser.add_argument('--quiet', '-q', action='store_true', help='only print results summary and failure logs')
     parser.add_argument('--nozmq', action='store_true', help='do not run the zmq tests')
     args, unknown_args = parser.parse_known_args()
@@ -241,6 +242,9 @@ def main():
 
     check_script_list(config["environment"]["SRCDIR"])
 
+    if not args.keepcache:
+        shutil.rmtree("%s/test/cache" % config["environment"]["BUILDDIR"], ignore_errors=True)
+
     run_tests(test_list, config["environment"]["SRCDIR"], config["environment"]["BUILDDIR"], config["environment"]["EXEEXT"], args.jobs, args.coverage, passon_args)
 
 def run_tests(test_list, src_dir, build_dir, exeext, jobs=1, enable_coverage=False, args=[]):