diff --git a/requirements.txt b/requirements.txt
index b73a7e45..426002dc 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,11 @@
-PyYAML>=3.10
-simplejson>=3.3.1
-netifaces>=0.8
-netaddr>=0.7.10
-Jinja2>=2.7.2
-six>=1.5.2
-dnspython
+# 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.
+PyYAML>=3.1.0
+simplejson>=2.2.0
+netifaces>=0.10.4
+netaddr>=0.7.12,!=0.7.16
+Jinja2>=2.6  # BSD License (3 clause)
+six>=1.9.0
+dnspython>=1.12.0
+psutil>=1.1.1,<2.0.0
diff --git a/test-requirements.txt b/test-requirements.txt
index ff4fb63b..3af44d73 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -1,7 +1,8 @@
-testtools
-coverage
-mock
-flake8==2.1.0
-# No version required
+# 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.
+coverage>=3.6
+mock>=1.2
+flake8>=2.2.4,<=2.4.1
+os-testr>=0.4.1
 charm-tools
-os-testr
diff --git a/tox.ini b/tox.ini
index 6bdf5757..4e328e48 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,4 @@
 [tox]
-# Default to current LTS
 envlist = lint,py27
 skipsdist = True