diff --git a/opencadd/structure/superposition/engines/base.py b/opencadd/structure/superposition/engines/base.py
index 215cef72..1aefd196 100644
--- a/opencadd/structure/superposition/engines/base.py
+++ b/opencadd/structure/superposition/engines/base.py
@@ -29,8 +29,8 @@ def calculate(self, structures, *args, **kwargs):
         """
         self._safety_checks()
         assert (
-            len(structures) == 2, 
-            "This method can only be used for two structures at the same time, for now"
+            len(structures) == 2,
+            "This method can only be used for two structures at the same time, for now",
         )
         return self._calculate(structures, *args, **kwargs)