diff --git a/integrators/_details/physicalToMathematical.py b/integrators/_details/physicalToMathematical.py
index 15b0fa7dd2e27ae09fbe4367ed207cc4f416c1b1..5f1b9e05d114b9ec3de13bc2cb4a200b0741b811 100644
--- a/integrators/_details/physicalToMathematical.py
+++ b/integrators/_details/physicalToMathematical.py
@@ -108,7 +108,11 @@ def Compute_Cst(self):
 def ConvertAppliedField(self):
   import types
   from ngsolve import CoefficientFunction, x, y, z
+
   if(self.parameters.H_ext == None):
+    self._hext_cf = CoefficientFunction((0, 0, 0))
+    self._hext_impl_cf = CoefficientFunction((0, 0, 0))
+    self._hext_mp_cf = CoefficientFunction((0, 0, 0))
     return
   
   tScale = self.parameters.gamma0 * self.parameters.Ms