diff --git a/build/docker/centos6/Dockerfile b/build/docker/centos6/Dockerfile
index aa19731..5567ab7 100644
--- a/build/docker/centos6/Dockerfile
+++ b/build/docker/centos6/Dockerfile
@@ -41,7 +41,9 @@
     && yum clean all
 
 # optional dependencies
-RUN pip install ipaddress backports.ssl_match_hostname tornado
+# skipping ipaddress and backports.ssl_match_hostname to test legacy callback
+# RUN pip install ipaddress backports.ssl_match_hostname tornado
+RUN pip install tornado
 
 # CMake
 RUN curl -sSL https://cmake.org/files/v3.4/cmake-3.4.1.tar.gz | tar -xz && \