diff --git a/doc/source/conf.py b/doc/source/conf.py
index daa549000..0c0ce5036 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -35,6 +35,7 @@ extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.graphviz',
               'oslosphinx',
               "ext.support_matrix",
+              'sphinxcontrib.seqdiag',
               ]
 
 todo_include_todos = True
diff --git a/test-requirements.txt b/test-requirements.txt
index d560ead9c..147dc7b8f 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -16,6 +16,7 @@ python-ironicclient>=0.6.0
 python-subunit>=0.0.18
 requests-mock>=0.6.0 # Apache-2.0
 sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2
+sphinxcontrib-seqdiag
 oslosphinx>=2.5.0 # Apache-2.0
 oslotest>=1.5.1 # Apache-2.0
 testrepository>=0.0.18