diff --git a/test-requirements.txt b/test-requirements.txt
index a7fdd1cf09..233651b582 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -18,6 +18,9 @@ testtools>=1.4.0
 # Doc requirements
 sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2
 sphinxcontrib-pecanwsme>=0.8
+# NOTE(tonyb): Pillow isn't used directly but it's needed for
+# sphinxcontrib-seqdiag.  Make sure we honnor g-r caps
+Pillow>=2.4.0,<3.0.0 # MIT
 sphinxcontrib-seqdiag
 oslosphinx>=2.5.0 # Apache-2.0