diff --git a/devstack-vm-gate-wrap.sh b/devstack-vm-gate-wrap.sh
index 08c509f5..37685e7e 100755
--- a/devstack-vm-gate-wrap.sh
+++ b/devstack-vm-gate-wrap.sh
@@ -355,6 +355,9 @@ export DEVSTACK_GATE_REQS_INTEGRATION=${DEVSTACK_GATE_REQS_INTEGRATION:-0}
 # in global requirements
 export REQUIREMENTS_MODE=${REQUIREMENTS_MODE:-strict}
 
+# Set to False to disable USE_CONSTRAINTS and run without known-good test pins.
+export USE_CONSTRAINTS=${USE_CONSTRAINTS:-True}
+
 # Set to 0 to disable clean logs enforcement (3rd party CI might want to do this
 # until they get their driver cleaned up)
 export DEVSTACK_GATE_CLEAN_LOGS=${DEVSTACK_GATE_CLEAN_LOGS:-1}
diff --git a/devstack-vm-gate.sh b/devstack-vm-gate.sh
index d1953d73..6a52ed6f 100755
--- a/devstack-vm-gate.sh
+++ b/devstack-vm-gate.sh
@@ -180,7 +180,12 @@ LOG_COLOR=False
 # Don't reset the requirements.txt files after g-r updates
 UNDO_REQUIREMENTS=False
 # Set to soft if the project is using libraries not in g-r
+# (pre-liberty)
 REQUIREMENTS_MODE=${REQUIREMENTS_MODE}
+# Set to False to disable the use of upper-constraints.txt
+# if you want to experience the wild freedom of uncapped
+# dependencies from PyPI
+USE_CONSTRAINTS=${USE_CONSTRAINTS}
 CINDER_PERIODIC_INTERVAL=10
 export OS_NO_CACHE=True
 CEILOMETER_BACKEND=$DEVSTACK_GATE_CEILOMETER_BACKEND