diff --git a/python3/src/stlib3/physics/constraints/fixedbox.py b/python3/src/stlib3/physics/constraints/fixedbox.py
index 0a43319..9cc9f28 100644
--- a/python3/src/stlib3/physics/constraints/fixedbox.py
+++ b/python3/src/stlib3/physics/constraints/fixedbox.py
@@ -35,7 +35,7 @@ def FixedBox(applyTo=None, atPositions=[-1.0, -1.0, -1.0, 1.0, 1.0, 1.0],
     else:
         c.addObject('BoxROI', position=position, name='BoxROI', box=atPositions, drawBoxes=doVisualization, doUpdate=doRecomputeDuringSimulation)
 
-    c.addObject('RestShapeSpringsForceField', points='@BoxROI.indices', stiffness=1e12)
+    c.addObject('FixedWeakConstraint', indices='@BoxROI.indices', stiffness=1e12)
     return c
 
 def createScene(rootNode):
diff --git a/python3/src/stlib3/physics/constraints/fixedbox_prefab.py b/python3/src/stlib3/physics/constraints/fixedbox_prefab.py
index a8b537f..84c7acc 100644
--- a/python3/src/stlib3/physics/constraints/fixedbox_prefab.py
+++ b/python3/src/stlib3/physics/constraints/fixedbox_prefab.py
@@ -41,7 +41,7 @@ def __init__(self, *args, **kwargs):
 
     def init(self):
         self.addObject('BoxROI', name='BoxROI', box=self.boxCoords, drawBoxes=self.showBox)
-        self.addObject('RestShapeSpringsForceField', points='@BoxROI.indices', stiffness=1e12)
+        self.addObject('FixedWeakConstraint', indices='@BoxROI.indices', stiffness=1e12)
 
 
 def createScene(rootnode):