diff --git a/jmclient/jmclient/configure.py b/jmclient/jmclient/configure.py
index b56273db0..497bff0de 100644
--- a/jmclient/jmclient/configure.py
+++ b/jmclient/jmclient/configure.py
@@ -410,7 +410,8 @@ def jm_single():
 cjfee_factor = 0.1
 
 # [satoshis, any integer] / the average transaction fee you're adding to coinjoin transactions
-txfee_contribution = 100
+# (note: this will soon be deprecated; leave at zero)
+txfee_contribution = 0
 
 # [fraction, 0-1] / variance around the average fee. Ex: 1000 fee, 0.2 var = fee is btw 800-1200
 txfee_contribution_factor = 0.3
diff --git a/jmclient/jmclient/maker.py b/jmclient/jmclient/maker.py
index d790dc2f7..89ec9df01 100644
--- a/jmclient/jmclient/maker.py
+++ b/jmclient/jmclient/maker.py
@@ -215,7 +215,11 @@ def verify_unsigned_tx(self, tx, offerinfo):
         my_total_in = sum([va['value'] for va in utxos.values()])
         real_cjfee = calc_cj_fee(ordertype, cjfee, amount)
         expected_change_value = (my_total_in - amount - txfee + real_cjfee)
-        jlog.info('potentially earned = {}'.format(btc.amount_to_str(real_cjfee - txfee)))
+        potentially_earned = real_cjfee - txfee
+        if potentially_earned < 0:
+            return (False, "A negative earning was calculated: {}.".format(
+                potentially_earned))
+        jlog.info('potentially earned = {}'.format(btc.amount_to_str(potentially_earned)))
         jlog.info('mycjaddr, mychange = {}, {}'.format(cjaddr, changeaddr))
 
         #The remaining checks are needed to ensure
diff --git a/jmdaemon/jmdaemon/daemon_protocol.py b/jmdaemon/jmdaemon/daemon_protocol.py
index 5daf4090b..60b1294c0 100644
--- a/jmdaemon/jmdaemon/daemon_protocol.py
+++ b/jmdaemon/jmdaemon/daemon_protocol.py
@@ -771,9 +771,11 @@ def on_order_fill(self, nick, oid, amount, taker_pk, commit):
         offer_s = [o for o in self.offerlist if o['oid'] == oid]
         if len(offer_s) == 0:
             self.mcc.send_error(nick, 'oid not found')
+            return
         offer = offer_s[0]
         if amount < offer['minsize'] or amount > offer['maxsize']:
             self.mcc.send_error(nick, 'amount out of range')
+            return
         #prepare a pubkey for this valid transaction
         kp = init_keypair()
         try: