diff --git a/feflow/utils/hybrid_topology.py b/feflow/utils/hybrid_topology.py
index 188125d1..35decf7c 100644
--- a/feflow/utils/hybrid_topology.py
+++ b/feflow/utils/hybrid_topology.py
@@ -2698,14 +2698,17 @@ def _create_hybrid_topology(self):
         # In the first instance, create a list of necessary atoms from
         # both old & new Topologies
         atom_list = []
+        # iterate once over the topologies for speed
+        old_topology_atoms = list(self._old_topology.atoms())
+        new_topology_atoms = list(self._new_topology.atoms())
 
         for pidx in range(self.hybrid_system.getNumParticles()):
             if pidx in self._hybrid_to_old_map:
                 idx = self._hybrid_to_old_map[pidx]
-                atom_list.append(list(self._old_topology.atoms())[idx])
+                atom_list.append(old_topology_atoms[idx])
             else:
                 idx = self._hybrid_to_new_map[pidx]
-                atom_list.append(list(self._new_topology.atoms())[idx])
+                atom_list.append(new_topology_atoms[idx])
 
         # Now we loop over the atoms and add them in alongside chains & resids