diff --git a/src/sire/morph/_repex.py b/src/sire/morph/_repex.py
index d350a4870..8edbd6057 100644
--- a/src/sire/morph/_repex.py
+++ b/src/sire/morph/_repex.py
@@ -104,8 +104,8 @@ def replica_exchange(
         pressure1 = ensemble1.pressure()
 
         delta = beta1 * (
-            nrgs1[1] - nrgs1[0] - (pressure1 * (volume1 - volume0) * N_A)
-        ) + beta0 * (nrgs0[0] - nrgs0[1] - (pressure0 * (volume0 - volume1) * N_A))
+            (nrgs1[1] - nrgs1[0]) + (pressure1 * (volume1 - volume0) * N_A)
+        ) + beta0 * ((nrgs0[0] - nrgs0[1]) + (pressure0 * (volume0 - volume1) * N_A))
 
     from math import exp