diff --git a/test/functional/dbcrash.py b/test/functional/dbcrash.py
--- a/test/functional/dbcrash.py
+++ b/test/functional/dbcrash.py
@@ -62,7 +62,7 @@
         self.node2_args = ["-dbcrashratio=24", "-dbcache=16"] + self.base_args
 
         # Node3 is a normal node with default args, except will mine full blocks
-        self.node3_args = ["-blockmaxweight=4000000"]
+        self.node3_args = ["-blockmaxsize=32000000"]
         self.extra_args = [self.node0_args, self.node1_args,
                            self.node2_args, self.node3_args]
 
diff --git a/test/functional/test_framework/test_node.py b/test/functional/test_framework/test_node.py
--- a/test/functional/test_framework/test_node.py
+++ b/test/functional/test_framework/test_node.py
@@ -168,7 +168,13 @@
     def calculate_fee(self, tx):
         # Relay fee is in satoshis per KB.  Thus the 1000, and the COIN added
         # to get back to an amount of satoshis.
-        return int(self.relay_fee() / 1000 * tx.billable_size() * COIN)
+        billable_size_estimate = tx.billable_size()
+        # Add some padding for signatures
+        # NOTE: Fees must be calculated before signatures are added,
+        # so they will never be included in the billable_size above.
+        billable_size_estimate += len(tx.vin) * 81
+
+        return int(self.relay_fee() / 1000 * billable_size_estimate * COIN)
 
     def calculate_fee_from_txid(self, txid):
         ctx = FromHex(CTransaction(), self.getrawtransaction(txid))