diff --git a/requirements.txt b/requirements.txt
index 72be9a9c1e..bfc5b19a2a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,10 @@
+# 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.
+
+# pbr should be first
 pbr>=0.6,!=0.7,<1.0
+
 alembic>=0.6.4
 anyjson>=0.3.3
 argparse
diff --git a/test-requirements.txt b/test-requirements.txt
index 44b429c04e..4441a35757 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -1,3 +1,8 @@
+# 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.
+
+# hacking should be first
 hacking>=0.9.2,<0.10
 
 coverage>=3.6