diff --git a/test/cpp/interop/client.cc b/test/cpp/interop/client.cc
index ee64716f3f6..cb9b396beb5 100644
--- a/test/cpp/interop/client.cc
+++ b/test/cpp/interop/client.cc
@@ -46,7 +46,7 @@
 #include "test/cpp/util/test_config.h"
 
 DEFINE_bool(use_tls, false, "Whether to use tls.");
-DEFINE_bool(use_test_ca, true, "False to use SSL roots for google");
+DEFINE_bool(use_test_ca, false, "False to use SSL roots for google");
 DEFINE_int32(server_port, 0, "Server port.");
 DEFINE_string(server_host, "127.0.0.1", "Server host to connect to");
 DEFINE_string(server_host_override, "foo.test.google.fr",
diff --git a/tools/gce_setup/grpc_docker.sh b/tools/gce_setup/grpc_docker.sh
index 1ac0209e278..e50706ec74b 100755
--- a/tools/gce_setup/grpc_docker.sh
+++ b/tools/gce_setup/grpc_docker.sh
@@ -1477,7 +1477,7 @@ grpc_cloud_prod_auth_compute_engine_creds_gen_node_cmd() {
 #   cmd=$($grpc_gen_test_cmd $flags)
 grpc_interop_gen_cxx_cmd() {
     local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls";
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls --use_test_ca";
     local the_cmd="$cmd_prefix $test_script $@";
     echo $the_cmd
 }
@@ -1489,7 +1489,7 @@ grpc_interop_gen_cxx_cmd() {
 #   cmd=$($grpc_gen_test_cmd $flags)
 grpc_cloud_prod_gen_cxx_cmd() {
     local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls --use_test_ca=false";
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls";
     local gfe_flags=$(_grpc_prod_gfe_flags)
     local the_cmd="$cmd_prefix $test_script $gfe_flags $@";
     echo $the_cmd
@@ -1502,7 +1502,7 @@ grpc_cloud_prod_gen_cxx_cmd() {
 #   cmd=$($grpc_gen_test_cmd $flags)
 grpc_cloud_prod_auth_service_account_creds_gen_cxx_cmd() {
     local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls --use_test_ca=false";
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls";
     local gfe_flags=$(_grpc_prod_gfe_flags)
     local added_gfe_flags=$(_grpc_svc_acc_test_flags)
     local the_cmd="$cmd_prefix $test_script $gfe_flags $added_gfe_flags $@";
@@ -1516,7 +1516,7 @@ grpc_cloud_prod_auth_service_account_creds_gen_cxx_cmd() {
 #   cmd=$($grpc_gen_test_cmd $flags)
 grpc_cloud_prod_auth_compute_engine_creds_gen_cxx_cmd() {
     local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls --use_test_ca=false";
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls";
     local gfe_flags=$(_grpc_prod_gfe_flags)
     local added_gfe_flags=$(_grpc_gce_test_flags)
     local the_cmd="$cmd_prefix $test_script $gfe_flags $added_gfe_flags $@";
@@ -1530,7 +1530,7 @@ grpc_cloud_prod_auth_compute_engine_creds_gen_cxx_cmd() {
 #   cmd=$($grpc_gen_test_cmd $flags)
 grpc_cloud_prod_auth_jwt_token_creds_gen_cxx_cmd() {
     local cmd_prefix="sudo docker run grpc/cxx";
-    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls --use_test_ca=false";
+    local test_script="/var/local/git/grpc/bins/opt/interop_client --use_tls";
     local gfe_flags=$(_grpc_prod_gfe_flags)
     local added_gfe_flags=$(_grpc_jwt_token_test_flags)
     local the_cmd="$cmd_prefix $test_script $gfe_flags $added_gfe_flags $@";
diff --git a/tools/run_tests/run_interop_tests.py b/tools/run_tests/run_interop_tests.py
index 39c9e53ce7f..209270f0c62 100755
--- a/tools/run_tests/run_interop_tests.py
+++ b/tools/run_tests/run_interop_tests.py
@@ -74,11 +74,11 @@ class CXXLanguage:
 
   def cloud_to_prod_args(self):
     return (self.client_cmdline_base + _CLOUD_TO_PROD_BASE_ARGS +
-            ['--use_tls=true','--use_test_ca=false'])
+            ['--use_tls=true'])
 
   def cloud_to_cloud_args(self):
     return (self.client_cmdline_base + _CLOUD_TO_CLOUD_BASE_ARGS +
-            ['--use_tls=true'])
+            ['--use_tls=true', '--use_test_ca=true'])
 
   def cloud_to_prod_env(self):
     return {}