diff --git a/tools/dockerfile/grpc_artifact_centos6_x64/Dockerfile b/tools/dockerfile/grpc_artifact_centos6_x64/Dockerfile
index d60d591852d..e765c876165 100644
--- a/tools/dockerfile/grpc_artifact_centos6_x64/Dockerfile
+++ b/tools/dockerfile/grpc_artifact_centos6_x64/Dockerfile
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 # Docker file for building gRPC artifacts.
+# Updated: 2020-06-16
 
 ##################
 # Base
diff --git a/tools/dockerfile/grpc_artifact_centos6_x86/Dockerfile b/tools/dockerfile/grpc_artifact_centos6_x86/Dockerfile
index f03cdd441b1..3e71c5439a5 100644
--- a/tools/dockerfile/grpc_artifact_centos6_x86/Dockerfile
+++ b/tools/dockerfile/grpc_artifact_centos6_x86/Dockerfile
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 # Docker file for building gRPC artifacts.
+# Updated: 2020-06-16
 
 ##################
 # Base