diff --git a/tools/pip_install.sh b/tools/pip_install.sh
index 7596c16..c7568eb 100755
--- a/tools/pip_install.sh
+++ b/tools/pip_install.sh
@@ -21,11 +21,7 @@ horizon_installed=$(echo "import horizon" | python 2>/dev/null ; echo $?)
 
 set -e
 
-install_cmd="pip install"
-if [ "$1" = "constrained" ]; then
-    install_cmd="$install_cmd $2"
-    shift
-fi
+install_cmd="pip install $1"
 shift
 
 if [ $horizon_installed -eq 0 ]; then
diff --git a/tox.ini b/tox.ini
index aafe228..2499a3d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,7 +5,9 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
-install_command = {toxinidir}/tools/pip_install.sh unconstrained {opts} {packages}
+install_command = {toxinidir}/tools/pip_install.sh \
+                -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} \
+                 {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
@@ -20,7 +22,9 @@ commands = flake8
 
 [testenv:venv]
 # This target does not use script since we do not need to install horizon.
-install_command = pip install -U --force-reinstall {opts} {packages}
+install_command = pip install \
+                -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} \
+                -U --force-reinstall {opts} {packages}
 commands = {posargs}
 
 # Django-1.8 is LTS