diff --git a/dass/pde.py b/dass/pde.py
index bb7f3a6..3c44774 100644
--- a/dass/pde.py
+++ b/dass/pde.py
@@ -1,4 +1,5 @@
 """Partial Differential Equations to use as forward models."""
+
 from typing import Optional
 
 import numpy as np