diff --git a/doc/requirements.txt b/doc/requirements.txt
index 8541fe38677d..77fc36caecc3 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,3 +1,6 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, which may cause wedges in the gate later.
 sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
 sphinxcontrib-actdiag>=0.8.5 # BSD
 sphinxcontrib-seqdiag>=0.8.4 # BSD
diff --git a/requirements.txt b/requirements.txt
index b9fff722699a..e34ac84fc7cf 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,7 +10,7 @@ Jinja2>=2.10 # BSD License (3 clause)
 keystonemiddleware>=4.17.0 # Apache-2.0
 lxml!=3.7.0,>=3.4.1 # BSD
 Routes>=2.3.1 # MIT
-cryptography!=2.0,>=1.9 # BSD/Apache-2.0
+cryptography>=2.1 # BSD/Apache-2.0
 WebOb>=1.7.1 # MIT
 greenlet>=0.4.10 # MIT
 PasteDeploy>=1.5.0 # MIT