diff --git a/src/bayesvalidrox/surrogate_models/engine.py b/src/bayesvalidrox/surrogate_models/engine.py
index 6f14cf3e82ab32e3aa4fdbf991ec692627c8e994..ecc9e9485e53b2174ae5c9cfc8c7ebf1676aa5d0 100644
--- a/src/bayesvalidrox/surrogate_models/engine.py
+++ b/src/bayesvalidrox/surrogate_models/engine.py
@@ -1016,7 +1016,7 @@ class Engine:
             RMSE of the standard deviations
 
         """
-        if self.Model.mc_reference is None:
+        if self.Model.mc_reference == {}:
             raise AttributeError('Model.mc_reference needs to be given to calculate the surrogate error!')
         # Compute the mean and std based on the MetaModel
         pce_means, pce_stds = self.MetaModel._compute_pce_moments()
diff --git a/tests/test_engine.py b/tests/test_engine.py
index 820de5b79851c688c8d2adcb5a66ed790937e0db..ae36047c5b24f32ba8592125d2d56e9d98b8505a 100644
--- a/tests/test_engine.py
+++ b/tests/test_engine.py
@@ -34,7 +34,7 @@ import pandas as pd
 import pytest
 import sys
 
-sys.path.append("src/")
+sys.path.append("../src/")
 
 from bayesvalidrox.surrogate_models.inputs import Input
 from bayesvalidrox.surrogate_models.exp_designs import ExpDesigns