# UNDF: UNDF-2026-000000919
--- a/electrum/address_synchronizer.py
+++ b/electrum/address_synchronizer.py
@@ -450,8 +450,9 @@ class AddressSynchronizer(Logger):
     @with_lock
     def receive_history_callback(self, addr: str, hist, tx_fees: Dict[str, int]):
         old_hist = self.get_address_history(addr)
+        hist_set = set(hist)
         for tx_hash, height in old_hist.items():
-            if (tx_hash, height) not in hist:
+            if (tx_hash, height) not in hist_set:
                 # make tx local
                 self.unverified_tx.pop(tx_hash, None)
                 self.unconfirmed_tx.pop(tx_hash, None)