diff --git a/hysop/operator/base/custom_symbolic_operator.py b/hysop/operator/base/custom_symbolic_operator.py
index 440d7eedc99c48f4ffd6c5e91e2cc7a1a3511b49..f3f42c9f33eb22e25ced23e79327b8078105b9e1 100644
--- a/hysop/operator/base/custom_symbolic_operator.py
+++ b/hysop/operator/base/custom_symbolic_operator.py
@@ -653,7 +653,7 @@ class SymbolicExpressionParser(object):
     @classmethod
     def parse_subexpr(cls, variables, info, expr):
         if isinstance(expr, npw.ndarray):
-            assert expr.ndim == 0
+            assert expr.ndim == 0, expr
             expr = expr.tolist()
         
         if isinstance(expr, (str, int,long,float,complex,npw.number)):
diff --git a/hysop/simulation.py b/hysop/simulation.py
index 273ffd406948c0dfc01c85b7880d7171eaeee731..f7d4d506b70dcbd2335b4cbf7eebbb87f2178859 100644
--- a/hysop/simulation.py
+++ b/hysop/simulation.py
@@ -138,8 +138,9 @@ class Simulation(object):
 
         dt_name = '{}_dt'.format(name) if (name is not None) else 'dt'
         if (dt is None):
-            dt = ScalarParameter(name=dt_name, dtype=HYSOP_REAL, 
-                    min_value=np.finfo(HYSOP_REAL).eps,
+            dtype = t.dtype if (t is not None) else HYSOP_REAL
+            dt = ScalarParameter(name=dt_name, dtype=dtype, 
+                    min_value=np.finfo(dtype).eps,
                     initial_value=dt0, quiet=quiet)
         else:
             dt.value = dt0