diff --git a/electrum/address_synchronizer.py b/electrum/address_synchronizer.py
index 6911b2e8c..ff6a61c57 100644
--- a/electrum/address_synchronizer.py
+++ b/electrum/address_synchronizer.py
@@ -855,7 +855,8 @@ class AddressSynchronizer(Logger):
             excluded_coins = set()
         assert isinstance(excluded_coins, set), f"excluded_coins should be set, not {type(excluded_coins)}"
 
-        cache_key = sha256(''.join(sorted(domain)) + ''.join(excluded_coins))
+        cache_key = sha256(','.join(sorted(domain)) + ';'
+                           + ','.join(sorted(excluded_coins)))
         cached_value = self._get_balance_cache.get(cache_key)
         if cached_value:
             return cached_value