diff --git a/openmmml/mlpotential.py b/openmmml/mlpotential.py
index 51ed8cf..800ece8 100644
--- a/openmmml/mlpotential.py
+++ b/openmmml/mlpotential.py
@@ -299,6 +299,8 @@ def createMixedSystem(self,
                     internalNonbonded.addPerBondParameter('chargeProd')
                     internalNonbonded.addPerBondParameter('sigma')
                     internalNonbonded.addPerBondParameter('epsilon')
+                    if force.usesPeriodicBoundaryConditions():
+                        internalNonbonded.setUsesPeriodicBoundaryConditions(True)
                     numParticles = system.getNumParticles()
                     atomCharge = [0]*numParticles
                     atomSigma = [0]*numParticles