diff --git a/desk/fitting/fitting_tools.py b/desk/fitting/fitting_tools.py
index 38a9d79c..d792fa33 100644
--- a/desk/fitting/fitting_tools.py
+++ b/desk/fitting/fitting_tools.py
@@ -93,7 +93,7 @@ def least2_liklihood(_data: np.ndarray, _model: np.ndarray) -> float:
         """
         # least squares fit
         _stat = np.nansum(np.square(_data - _model) / _model)
-        prob = np.exp(-0.5 * np.float128(_stat))
+        prob = np.exp(-0.5 * np.longdouble(_stat))
         return prob
 
     def fit_data(data: np.ndarray, model: np.ndarray) -> float: