diff --git a/electrum/address_synchronizer.py b/electrum/address_synchronizer.py
index f40e3fc37..ee4f8c51b 100644
--- a/electrum/address_synchronizer.py
+++ b/electrum/address_synchronizer.py
@@ -80,7 +80,7 @@ class AddressSynchronizer(Logger):
         # locks: if you need to take multiple ones, acquire them in the order they are defined here!
         self.lock = threading.RLock()
         self.transaction_lock = threading.RLock()
-        self.future_tx = {} # txid -> blocks remaining
+        self.future_tx = {}  # type: Dict[str, int]  # txid -> blocks remaining
         # Transactions pending verification.  txid -> tx_height. Access with self.lock.
         self.unverified_tx = defaultdict(int)
         # true when synchronized
@@ -566,7 +566,8 @@ class AddressSynchronizer(Logger):
             return cached_local_height
         return self.network.get_local_height() if self.network else self.db.get('stored_height', 0)
 
-    def add_future_tx(self, tx: Transaction, num_blocks):
+    def add_future_tx(self, tx: Transaction, num_blocks: int) -> None:
+        assert num_blocks > 0, num_blocks
         with self.lock:
             self.add_transaction(tx.txid(), tx)
             self.future_tx[tx.txid()] = num_blocks
@@ -581,9 +582,9 @@ class AddressSynchronizer(Logger):
                 height = self.unverified_tx[tx_hash]
                 return TxMinedInfo(height=height, conf=0)
             elif tx_hash in self.future_tx:
-                # FIXME this is ugly
-                conf = self.future_tx[tx_hash]
-                return TxMinedInfo(height=TX_HEIGHT_FUTURE, conf=conf)
+                num_blocks_remainining = self.future_tx[tx_hash]
+                assert num_blocks_remainining > 0, num_blocks_remainining
+                return TxMinedInfo(height=TX_HEIGHT_FUTURE, conf=-num_blocks_remainining)
             else:
                 # local transaction
                 return TxMinedInfo(height=TX_HEIGHT_LOCAL, conf=0)
diff --git a/electrum/util.py b/electrum/util.py
index 84598ee68..c60a29770 100644
--- a/electrum/util.py
+++ b/electrum/util.py
@@ -1024,7 +1024,7 @@ def ignore_exceptions(func):
 
 class TxMinedInfo(NamedTuple):
     height: int                        # height of block that mined tx
-    conf: Optional[int] = None         # number of confirmations (None means unknown)
+    conf: Optional[int] = None         # number of confirmations, SPV verified (None means unknown)
     timestamp: Optional[int] = None    # timestamp of block that mined tx
     txpos: Optional[int] = None        # position of tx in serialized block
     header_hash: Optional[str] = None  # hash of block that mined tx
diff --git a/electrum/wallet.py b/electrum/wallet.py
index da27c51c9..1919fc6b7 100644
--- a/electrum/wallet.py
+++ b/electrum/wallet.py
@@ -817,7 +817,9 @@ class Abstract_Wallet(AddressSynchronizer):
         conf = tx_mined_info.conf
         timestamp = tx_mined_info.timestamp
         if height == TX_HEIGHT_FUTURE:
-            return 2, 'in %d blocks'%conf
+            assert conf < 0, conf
+            num_blocks_remainining = -conf
+            return 2, f'in {num_blocks_remainining} blocks'
         if conf == 0:
             tx = self.db.get_transaction(tx_hash)
             if not tx: