diff --git a/global-requirements.txt b/global-requirements.txt
index d5b1a12d9b..3f8bffd773 100644
--- a/global-requirements.txt
+++ b/global-requirements.txt
@@ -421,7 +421,7 @@ selenium>=2.50.1  # Apache-2.0
 # Blacklist setuptools 34.0.0-34.3.2 due to https://github.com/pypa/setuptools/issues/951
 # Blacklist setuptools 36.2.0 due to https://github.com/pypa/setuptools/issues/1086
 setuptools>=16.0,!=24.0.0,!=34.0.0,!=34.0.1,!=34.0.2,!=34.0.3,!=34.1.0,!=34.1.1,!=34.2.0,!=34.3.0,!=34.3.1,!=34.3.2,!=36.2.0  # PSF/ZPL
-sphinx>=1.6.2  # BSD
+sphinx>=1.6.2,!=1.6.6  # BSD
 sphinx-testing>=0.7.2  # BSD License
 sphinxcontrib-actdiag>=0.8.5  # BSD
 sphinxcontrib-blockdiag>=1.5.4  # BSD
diff --git a/upper-constraints.txt b/upper-constraints.txt
index 43153a3b11..139a53ae80 100644
--- a/upper-constraints.txt
+++ b/upper-constraints.txt
@@ -365,7 +365,7 @@ python-consul===0.7.2
 seqdiag===0.9.5
 numpy===1.14.0
 repoze.who===2.3
-Sphinx===1.6.6
+Sphinx===1.6.5
 oslo.config===5.2.0
 tempest===17.2.0
 django-floppyforms===1.7.0