diff --git a/ensemble_md/replica_exchange_EE.py b/ensemble_md/replica_exchange_EE.py
index 46817c8..65606fd 100644
--- a/ensemble_md/replica_exchange_EE.py
+++ b/ensemble_md/replica_exchange_EE.py
@@ -833,7 +833,7 @@ def identify_swappable_pairs(self, states, state_ranges, dhdl_files, iteration=N
         """
         n_sim = len(states)
         sim_idx = list(range(n_sim))
-        states_for_swap = []
+        states_for_swap = {}
         if self.proposal == 'forced_swap':
             potential_swappables = []
             if iteration % 2 == 0:  # Swap up for self.n_sim - 1 swaps
@@ -842,24 +842,26 @@ def identify_swappable_pairs(self, states, state_ranges, dhdl_files, iteration=N
             else:  # and then swap down for self.n_sim - 1 swaps and repeat
                 for n in np.arange(1, n_sim-1, 2):
                     potential_swappables.append([n, n+1])
-            swap_index, swappables = [], []
+            swappables = []
+            swap_index = {}
             for swap in potential_swappables:
                 index, state = self._deter_swap_index(swap, dhdl_files, self.add_swappables)
                 if len(index) == 2:
-                    swap_index.append(index)
+                    swap_index[swap] = index
                     swappables.append(swap)
-                    states_for_swap.append(state)
+                    states_for_swap[swap] = state
         elif self.proposal == 'forced_random':
             potential_swappables = []
             for n in np.arange(0, n_sim-1,1):
                 potential_swappables.append([n, n+1])
-            swap_index, swappables = [], []
+            swappables = []
+            swap_index = {}
             for swap in potential_swappables:
                 index, state = self._deter_swap_index(swap, dhdl_files, self.add_swappables)
                 if len(index) == 2:
-                    swap_index.append(index)
+                    swap_index[swap] = index
                     swappables.append(swap)
-                    states_for_swap.append(state)
+                    states_for_swap[swap] = state
         else:
             all_pairs = list(combinations(sim_idx, 2))
 
@@ -1036,9 +1038,10 @@ def get_swapping_pattern(self, dhdl_files, states, iteration=None):
                     if swap_bool is True:
                         swap_list.append(swap)
                         if self.proposal == "forced_swap":
-                            swap_index_accept.append(swap_index[i])
-                            states_modified[swap[0]] = states_for_swap[i][0]
-                            states_modified[swap[1]] = states_for_swap[i][1]
+                            swap_index_accept.append(swap_index[swap])
+                            states_i = states_for_swap[swap]
+                            states_modified[swap[0]] = states_i[0]
+                            states_modified[swap[1]] = states_i[1]
                         else:
                             swap_index_accept.append([-1, -1])
                         # Determine which