diff --git a/stack.sh b/stack.sh
index ae14c80c68..db5e815f0a 100755
--- a/stack.sh
+++ b/stack.sh
@@ -679,6 +679,12 @@ fi
 
 # OpenStack uses a fair number of other projects.
 
+
+# Bring down global requirements before any use of pip_install. This is
+# necessary to ensure that the constraints file is in place before we
+# attempt to apply any constraints to pip installs.
+git_clone $REQUIREMENTS_REPO $REQUIREMENTS_DIR $REQUIREMENTS_BRANCH
+
 # Install package requirements
 # Source it so the entire environment is available
 echo_summary "Installing package prerequisites"