diff --git a/apstools/diffractometer.py b/apstools/diffractometer.py
index 330cf96fe..343a6b482 100644
--- a/apstools/diffractometer.py
+++ b/apstools/diffractometer.py
@@ -93,7 +93,7 @@ def undoLastConstraints(self):
     def _push_current_constraints(self):
         """push current constraints onto the stack"""
         constraints = {
-            m: Constraints(
+            m: Constraint(
                 *self.calc[m].limits,
                 self.calc[m].value,
                 self.calc[m].fit)