diff --git a/uniswap/uniswap.py b/uniswap/uniswap.py
index 5edbc85..1bc11d7 100644
--- a/uniswap/uniswap.py
+++ b/uniswap/uniswap.py
@@ -1436,7 +1436,7 @@ def _build_and_send_tx(
             tx_params = self._get_tx_params()
         transaction = function.build_transaction(tx_params)
 
-        if "gas" not in tx_params:
+        if "gas" not in transaction:
             # `use_estimate_gas` needs to be True for networks like Arbitrum (can't assume 250000 gas),
             # but it breaks tests for unknown reasons because estimate_gas takes forever on some tx's.
             # Maybe an issue with ganache? (got GC warnings once...)