diff --git a/phases/models/parallel_model.py b/phases/models/parallel_model.py
index 97c0ed7..03a5782 100644
--- a/phases/models/parallel_model.py
+++ b/phases/models/parallel_model.py
@@ -1,3 +1,4 @@
+import math
 import numpy as np
 from scipy.optimize import fsolve