diff --git a/requirements-py2.txt b/requirements-py2.txt
index fe897b7b2..0827e7ed0 100644
--- a/requirements-py2.txt
+++ b/requirements-py2.txt
@@ -2,6 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
+# See: https://bugs.launchpad.net/pbr/+bug/1384919 for why this is here...
 pbr>=0.6,!=0.7,<1.0
 
 # Packages needed for using this library.
diff --git a/requirements-py3.txt b/requirements-py3.txt
index f135eff4f..5f265dcc9 100644
--- a/requirements-py3.txt
+++ b/requirements-py3.txt
@@ -2,6 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
+# See: https://bugs.launchpad.net/pbr/+bug/1384919 for why this is here...
 pbr>=0.6,!=0.7,<1.0
 
 # Packages needed for using this library.