diff --git a/src/NanoParticleTools/inputs/nanoparticle.py b/src/NanoParticleTools/inputs/nanoparticle.py
index 20dee38..59c0999 100644
--- a/src/NanoParticleTools/inputs/nanoparticle.py
+++ b/src/NanoParticleTools/inputs/nanoparticle.py
@@ -141,8 +141,7 @@ def sites_in_bounds(self,
             center = [0, 0, 0]
 
         distances_from_center = np.linalg.norm(np.subtract(
-            site_coords, center),
-                                               axis=1)
+            site_coords, center), axis=1)
         return distances_from_center <= self.radius
 
     def __str__(self) -> str: