diff --git a/.testr.conf b/.testr.conf
index 5934641ef..516dbbc88 100644
--- a/.testr.conf
+++ b/.testr.conf
@@ -15,5 +15,5 @@ group_regex=.*(test_cert_setup|test_keystoneclient).+
 # a non-default (1 worker per available core) concurrency is desired, set
 # environment variable ``TEST_RUN_CONCURRENCY`` to the desired number of
 # workers.
-test_run_concurrency=echo ${TEST_RUN_CONCURRENCY:-1}
+test_run_concurrency=echo ${TEST_RUN_CONCURRENCY:-0}