diff --git a/src/minimization/stochastic_minimizer.py b/src/minimization/stochastic_minimizer.py
index 7201a4259ebe82773128eaf65b428669f80ac523..238f33bf1dbf3a95d04af7699f41943172ad0df9 100644
--- a/src/minimization/stochastic_minimizer.py
+++ b/src/minimization/stochastic_minimizer.py
@@ -72,7 +72,7 @@ class ADVIOptimizer(Minimizer):
             x = self._step(E.position, E.gradient)
             E = self._resample(x)
             myassert(isinstance(E, Energy))
-            myassert(x.domain, E.position.domain)
+            myassert(x.domain is E.position.domain)
         return E, convergence
 
     def reset(self):