diff --git a/carnot/tree_overlay.py b/carnot/tree_overlay.py
index cf24d8c..31aa6b4 100644
--- a/carnot/tree_overlay.py
+++ b/carnot/tree_overlay.py
@@ -8,7 +8,7 @@ import random
 
 def blake2b_hash(committee: Committee) -> bytes:
     hasher = blake2b(digest_size=32)
-    for member in committee:
+    for member in sorted(committee):
         hasher.update(member)
     return hasher.digest()