diff --git a/cluster/gce/config-test.sh b/cluster/gce/config-test.sh
index aa9d1c2365..3dd2ea0e0b 100755
--- a/cluster/gce/config-test.sh
+++ b/cluster/gce/config-test.sh
@@ -112,11 +112,11 @@ TEST_CLUSTER_API_CONTENT_TYPE="${TEST_CLUSTER_API_CONTENT_TYPE:-}"
 # ContentType used to store objects in underlying database.
 TEST_CLUSTER_STORAGE_CONTENT_TYPE="${TEST_CLUSTER_STORAGE_CONTENT_TYPE:-}"
 
-KUBELET_TEST_ARGS="--max-pods=110 --serialize-image-pulls=false --outofdisk-transition-frequency=0 ${TEST_CLUSTER_API_CONTENT_TYPE}"
-APISERVER_TEST_ARGS="--runtime-config=extensions/v1beta1 ${TEST_CLUSTER_DELETE_COLLECTION_WORKERS} ${TEST_CLUSTER_MAX_REQUESTS_INFLIGHT} ${TEST_CLUSTER_STORAGE_CONTENT_TYPE}"
-CONTROLLER_MANAGER_TEST_ARGS="${TEST_CLUSTER_RESYNC_PERIOD} ${TEST_CLUSTER_API_CONTENT_TYPE}"
-SCHEDULER_TEST_ARGS="${TEST_CLUSTER_API_CONTENT_TYPE}"
-KUBEPROXY_TEST_ARGS="${TEST_CLUSTER_API_CONTENT_TYPE}"
+KUBELET_TEST_ARGS="${KUBELET_TEST_ARGS:-} --max-pods=110 --serialize-image-pulls=false --outofdisk-transition-frequency=0 ${TEST_CLUSTER_API_CONTENT_TYPE}"
+APISERVER_TEST_ARGS="${APISERVER_TEST_ARGS:-} --runtime-config=extensions/v1beta1 ${TEST_CLUSTER_DELETE_COLLECTION_WORKERS} ${TEST_CLUSTER_MAX_REQUESTS_INFLIGHT} ${TEST_CLUSTER_STORAGE_CONTENT_TYPE}"
+CONTROLLER_MANAGER_TEST_ARGS="${CONTROLLER_MANAGER_TEST_ARGS:-} ${TEST_CLUSTER_RESYNC_PERIOD} ${TEST_CLUSTER_API_CONTENT_TYPE}"
+SCHEDULER_TEST_ARGS="${SCHEDULER_TEST_ARGS:-} ${TEST_CLUSTER_API_CONTENT_TYPE}"
+KUBEPROXY_TEST_ARGS="${KUBEPROXY_TEST_ARGS:-} ${TEST_CLUSTER_API_CONTENT_TYPE}"
 
 # Optional: Enable node logging.
 ENABLE_NODE_LOGGING="${KUBE_ENABLE_NODE_LOGGING:-true}"