diff --git a/core/src/apps/bitcoin/sign_tx/__init__.py b/core/src/apps/bitcoin/sign_tx/__init__.py
index 49715a8ff..34c98f163 100644
--- a/core/src/apps/bitcoin/sign_tx/__init__.py
+++ b/core/src/apps/bitcoin/sign_tx/__init__.py
@@ -10,7 +10,7 @@ if not utils.BITCOIN_ONLY:
     from . import bitcoinlike, decred, zcash
 
 if False:
-    from typing import Optional, Union
+    from typing import Protocol, Optional, Type, Union
 
     from protobuf import FieldCache
 
@@ -36,6 +36,19 @@ if False:
         TxAckPrevExtraData,
     ]
 
+    class SignerClass(Protocol):
+        def __init__(
+            self,
+            tx: SignTx,
+            keychain: Keychain,
+            coin: CoinInfo,
+            approver: Optional[approvers.Approver],
+        ) -> None:
+            ...
+
+        async def signer(self) -> None:
+            ...
+
 
 @with_keychain
 async def sign_tx(
@@ -45,15 +58,12 @@ async def sign_tx(
     coin: CoinInfo,
     authorization: Optional[CoinJoinAuthorization] = None,
 ) -> TxRequest:
+    approver: Optional[approvers.Approver] = None
     if authorization:
-        approver: approvers.Approver = approvers.CoinJoinApprover(
-            msg, coin, authorization
-        )
-    else:
-        approver = approvers.BasicApprover(msg, coin)
+        approver = approvers.CoinJoinApprover(msg, coin, authorization)
 
     if utils.BITCOIN_ONLY or coin.coin_name in BITCOIN_NAMES:
-        signer_class = bitcoin.Bitcoin
+        signer_class: Type[SignerClass] = bitcoin.Bitcoin
     else:
         if coin.decred:
             signer_class = decred.Decred
diff --git a/core/src/apps/bitcoin/sign_tx/approvers.py b/core/src/apps/bitcoin/sign_tx/approvers.py
index b2b1fa935..79b6dbb2c 100644
--- a/core/src/apps/bitcoin/sign_tx/approvers.py
+++ b/core/src/apps/bitcoin/sign_tx/approvers.py
@@ -2,7 +2,6 @@ from micropython import const
 
 from trezor import wire
 from trezor.messages import OutputScriptType
-from trezor.utils import ensure
 
 from apps.common import safety_checks
 
@@ -77,11 +76,6 @@ class Approver:
         self.weight.add_output(script_pubkey)
         self.total_out += txo.amount
 
-    async def add_decred_sstx_submission(
-        self, txo: TxOutput, script_pubkey: bytes
-    ) -> None:
-        raise NotImplementedError
-
     def add_orig_external_output(self, txo: TxOutput) -> None:
         self.orig_total_out += txo.amount
 
@@ -131,13 +125,6 @@ class BasicApprover(Approver):
         else:
             await helpers.confirm_output(txo, self.coin, self.amount_unit)
 
-    async def add_decred_sstx_submission(
-        self, txo: TxOutput, script_pubkey: bytes
-    ) -> None:
-        ensure(self.coin.decred)
-        await super().add_external_output(txo, script_pubkey, None)
-        await helpers.confirm_decred_sstx_submission(txo, self.coin, self.amount_unit)
-
     async def approve_tx(self, tx_info: TxInfo, orig_txs: List[OriginalTxInfo]) -> None:
         fee = self.total_in - self.total_out
 
diff --git a/core/src/apps/bitcoin/sign_tx/bitcoin.py b/core/src/apps/bitcoin/sign_tx/bitcoin.py
index 06631d106..f22ba6f60 100644
--- a/core/src/apps/bitcoin/sign_tx/bitcoin.py
+++ b/core/src/apps/bitcoin/sign_tx/bitcoin.py
@@ -73,12 +73,16 @@ class Bitcoin:
         tx: SignTx,
         keychain: Keychain,
         coin: CoinInfo,
-        approver: approvers.Approver,
+        approver: Optional[approvers.Approver],
     ) -> None:
         self.tx_info = TxInfo(self, helpers.sanitize_sign_tx(tx, coin))
         self.keychain = keychain
         self.coin = coin
-        self.approver = approver
+
+        if approver is not None:
+            self.approver = approver
+        else:
+            self.approver = approvers.BasicApprover(tx, coin)
 
         # set of indices of inputs which are segwit
         self.segwit: Set[int] = set()
diff --git a/core/src/apps/bitcoin/sign_tx/decred.py b/core/src/apps/bitcoin/sign_tx/decred.py
index 6a607b1e6..c27d15b12 100644
--- a/core/src/apps/bitcoin/sign_tx/decred.py
+++ b/core/src/apps/bitcoin/sign_tx/decred.py
@@ -11,6 +11,7 @@ from apps.common.writers import write_bitcoin_varint
 from .. import multisig, scripts_decred, writers
 from ..common import ecdsa_hash_pubkey, ecdsa_sign
 from . import approvers, helpers, progress
+from .approvers import BasicApprover
 from .bitcoin import Bitcoin
 
 DECRED_SERIALIZE_FULL = const(0 << 16)
@@ -37,6 +38,16 @@ if False:
     from .hash143 import Hash143
 
 
+class DecredApprover(BasicApprover):
+    async def add_decred_sstx_submission(
+        self, txo: TxOutput, script_pubkey: bytes
+    ) -> None:
+        # NOTE: The following calls Approver.add_external_output(), not BasicApprover.add_external_output().
+        # This is needed to skip calling helpers.confirm_output(), which is what BasicApprover would do.
+        await super(BasicApprover, self).add_external_output(txo, script_pubkey, None)
+        await helpers.confirm_decred_sstx_submission(txo, self.coin, self.amount_unit)
+
+
 class DecredHash:
     def __init__(self, h_prefix: HashWriter) -> None:
         self.h_prefix = h_prefix
@@ -65,11 +76,13 @@ class Decred(Bitcoin):
         tx: SignTx,
         keychain: Keychain,
         coin: CoinInfo,
-        approver: approvers.Approver,
+        approver: Optional[approvers.Approver],
     ) -> None:
         ensure(coin.decred)
         self.h_prefix = HashWriter(blake256())
 
+        ensure(approver is None)
+        approver = DecredApprover(tx, coin)
         super().__init__(tx, keychain, coin, approver)
 
         self.write_tx_header(self.serialized_tx, self.tx_info.tx, witness_marker=True)
@@ -233,6 +246,8 @@ class Decred(Bitcoin):
         return scripts_decred.output_script_paytoopreturn(op_return_data)
 
     async def approve_staking_ticket(self) -> None:
+        assert isinstance(self.approver, DecredApprover)
+
         if self.tx_info.tx.outputs_count != 3:
             raise wire.DataError("Ticket has wrong number of outputs.")
 
diff --git a/core/tests/test_apps.bitcoin.segwit.signtx.native_p2wpkh.py b/core/tests/test_apps.bitcoin.segwit.signtx.native_p2wpkh.py
index 405cfb695..afea4d414 100644
--- a/core/tests/test_apps.bitcoin.segwit.signtx.native_p2wpkh.py
+++ b/core/tests/test_apps.bitcoin.segwit.signtx.native_p2wpkh.py
@@ -30,7 +30,6 @@ from apps.common import coins
 from apps.common.keychain import Keychain
 from apps.bitcoin.keychain import get_schemas_for_coin
 from apps.bitcoin.sign_tx import helpers, bitcoin
-from apps.bitcoin.sign_tx.approvers import BasicApprover
 
 
 EMPTY_SERIALIZED = TxRequestSerializedType(serialized_tx=bytearray())
@@ -160,8 +159,7 @@ class TestSignSegwitTxNativeP2WPKH(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoin.Bitcoin(tx, keychain, coin, approver).signer()
+        signer = bitcoin.Bitcoin(tx, keychain, coin, None).signer()
         for request, response in chunks(messages, 2):
             res = signer.send(request)
             if isinstance(res, tuple):
@@ -289,8 +287,7 @@ class TestSignSegwitTxNativeP2WPKH(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoin.Bitcoin(tx, keychain, coin, approver).signer()
+        signer = bitcoin.Bitcoin(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             response = signer.send(request)
             if isinstance(response, tuple):
@@ -350,8 +347,7 @@ class TestSignSegwitTxNativeP2WPKH(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoin.Bitcoin(tx, keychain, coin, approver).signer()
+        signer = bitcoin.Bitcoin(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             if expected_response is None:
                 with self.assertRaises(wire.DataError):
diff --git a/core/tests/test_apps.bitcoin.segwit.signtx.native_p2wpkh_grs.py b/core/tests/test_apps.bitcoin.segwit.signtx.native_p2wpkh_grs.py
index 319a57bb6..1366eadab 100644
--- a/core/tests/test_apps.bitcoin.segwit.signtx.native_p2wpkh_grs.py
+++ b/core/tests/test_apps.bitcoin.segwit.signtx.native_p2wpkh_grs.py
@@ -29,7 +29,6 @@ from apps.common import coins
 from apps.common.keychain import Keychain
 from apps.bitcoin.keychain import get_schemas_for_coin
 from apps.bitcoin.sign_tx import bitcoinlike, helpers
-from apps.bitcoin.sign_tx.approvers import BasicApprover
 
 
 EMPTY_SERIALIZED = TxRequestSerializedType(serialized_tx=bytearray())
@@ -161,8 +160,7 @@ class TestSignSegwitTxNativeP2WPKH_GRS(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, approver).signer()
+        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             response = signer.send(request)
             if isinstance(response, tuple):
@@ -290,8 +288,7 @@ class TestSignSegwitTxNativeP2WPKH_GRS(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, approver).signer()
+        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             response = signer.send(request)
             if isinstance(response, tuple):
diff --git a/core/tests/test_apps.bitcoin.segwit.signtx.p2wpkh_in_p2sh.py b/core/tests/test_apps.bitcoin.segwit.signtx.p2wpkh_in_p2sh.py
index 2b2d5edad..8fc6fd41c 100644
--- a/core/tests/test_apps.bitcoin.segwit.signtx.p2wpkh_in_p2sh.py
+++ b/core/tests/test_apps.bitcoin.segwit.signtx.p2wpkh_in_p2sh.py
@@ -30,7 +30,6 @@ from apps.common import coins
 from apps.common.keychain import Keychain
 from apps.bitcoin.keychain import get_schemas_for_coin
 from apps.bitcoin.sign_tx import bitcoin, helpers
-from apps.bitcoin.sign_tx.approvers import BasicApprover
 
 
 EMPTY_SERIALIZED = TxRequestSerializedType(serialized_tx=bytearray())
@@ -157,8 +156,7 @@ class TestSignSegwitTxP2WPKHInP2SH(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoin.Bitcoin(tx, keychain, coin, approver).signer()
+        signer = bitcoin.Bitcoin(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             response = signer.send(request)
             if isinstance(response, tuple):
@@ -294,8 +292,7 @@ class TestSignSegwitTxP2WPKHInP2SH(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoin.Bitcoin(tx, keychain, coin, approver).signer()
+        signer = bitcoin.Bitcoin(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             response = signer.send(request)
             if isinstance(response, tuple):
@@ -401,8 +398,7 @@ class TestSignSegwitTxP2WPKHInP2SH(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoin.Bitcoin(tx, keychain, coin, approver).signer()
+        signer = bitcoin.Bitcoin(tx, keychain, coin, None).signer()
         i = 0
         messages_count = int(len(messages) / 2)
         for request, expected_response in chunks(messages, 2):
diff --git a/core/tests/test_apps.bitcoin.segwit.signtx.p2wpkh_in_p2sh_grs.py b/core/tests/test_apps.bitcoin.segwit.signtx.p2wpkh_in_p2sh_grs.py
index 95c88251b..e857955a5 100644
--- a/core/tests/test_apps.bitcoin.segwit.signtx.p2wpkh_in_p2sh_grs.py
+++ b/core/tests/test_apps.bitcoin.segwit.signtx.p2wpkh_in_p2sh_grs.py
@@ -29,7 +29,6 @@ from apps.common import coins
 from apps.common.keychain import Keychain
 from apps.bitcoin.keychain import get_schemas_for_coin
 from apps.bitcoin.sign_tx import bitcoinlike, helpers
-from apps.bitcoin.sign_tx.approvers import BasicApprover
 
 
 EMPTY_SERIALIZED = TxRequestSerializedType(serialized_tx=bytearray())
@@ -161,8 +160,7 @@ class TestSignSegwitTxP2WPKHInP2SH_GRS(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, approver).signer()
+        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             response = signer.send(request)
             if isinstance(response, tuple):
@@ -298,8 +296,7 @@ class TestSignSegwitTxP2WPKHInP2SH_GRS(unittest.TestCase):
 
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, approver).signer()
+        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             response = signer.send(request)
             if isinstance(response, tuple):
diff --git a/core/tests/test_apps.bitcoin.signtx.fee_threshold.py b/core/tests/test_apps.bitcoin.signtx.fee_threshold.py
index e44c21947..e8916c501 100644
--- a/core/tests/test_apps.bitcoin.signtx.fee_threshold.py
+++ b/core/tests/test_apps.bitcoin.signtx.fee_threshold.py
@@ -28,7 +28,6 @@ from apps.common import coins
 from apps.common.keychain import Keychain
 from apps.common.paths import AlwaysMatchingSchema
 from apps.bitcoin.sign_tx import bitcoin, helpers
-from apps.bitcoin.sign_tx.approvers import BasicApprover
 
 
 EMPTY_SERIALIZED = TxRequestSerializedType(serialized_tx=bytearray())
@@ -164,8 +163,7 @@ class TestSignTxFeeThreshold(unittest.TestCase):
         seed = bip39.seed('alcohol woman abuse must during monitor noble actual mixed trade anger aisle', '')
 
         keychain = Keychain(seed, coin_bitcoin.curve_name, [AlwaysMatchingSchema])
-        approver = BasicApprover(tx, coin_bitcoin)
-        signer = bitcoin.Bitcoin(tx, keychain, coin_bitcoin, approver).signer()
+        signer = bitcoin.Bitcoin(tx, keychain, coin_bitcoin, None).signer()
         for request, response in chunks(messages, 2):
             res = signer.send(request)
             if isinstance(res, tuple):
diff --git a/core/tests/test_apps.bitcoin.signtx.py b/core/tests/test_apps.bitcoin.signtx.py
index 24f819419..d2b384bfe 100644
--- a/core/tests/test_apps.bitcoin.signtx.py
+++ b/core/tests/test_apps.bitcoin.signtx.py
@@ -28,7 +28,6 @@ from apps.common import coins
 from apps.common.keychain import Keychain
 from apps.bitcoin.keychain import get_schemas_for_coin
 from apps.bitcoin.sign_tx import bitcoin, helpers
-from apps.bitcoin.sign_tx.approvers import BasicApprover
 
 
 EMPTY_SERIALIZED = TxRequestSerializedType(serialized_tx=bytearray())
@@ -110,8 +109,7 @@ class TestSignTx(unittest.TestCase):
         seed = bip39.seed('alcohol woman abuse must during monitor noble actual mixed trade anger aisle', '')
         ns = get_schemas_for_coin(coin_bitcoin)
         keychain = Keychain(seed, coin_bitcoin.curve_name, ns)
-        approver = BasicApprover(tx, coin_bitcoin)
-        signer = bitcoin.Bitcoin(tx, keychain, coin_bitcoin, approver).signer()
+        signer = bitcoin.Bitcoin(tx, keychain, coin_bitcoin, None).signer()
 
         for request, response in chunks(messages, 2):
             res = signer.send(request)
diff --git a/core/tests/test_apps.bitcoin.signtx_decred.py b/core/tests/test_apps.bitcoin.signtx_decred.py
index 61ce05122..ab2258edd 100644
--- a/core/tests/test_apps.bitcoin.signtx_decred.py
+++ b/core/tests/test_apps.bitcoin.signtx_decred.py
@@ -1,7 +1,7 @@
 from common import *
 
 from trezor.utils import chunks
-from trezor.crypto import bip32, bip39
+from trezor.crypto import bip39
 from trezor.messages.SignTx import SignTx
 from trezor.messages.TxAckInput import TxAckInput
 from trezor.messages.TxAckInputWrapper import TxAckInputWrapper
@@ -28,7 +28,6 @@ from apps.common import coins
 from apps.common.keychain import Keychain
 from apps.bitcoin.keychain import get_schemas_for_coin
 from apps.bitcoin.sign_tx import decred, helpers
-from apps.bitcoin.sign_tx.approvers import BasicApprover
 
 
 EMPTY_SERIALIZED = TxRequestSerializedType(serialized_tx=bytearray())
@@ -190,8 +189,7 @@ class TestSignTxDecred(unittest.TestCase):
         )
         ns = get_schemas_for_coin(coin_decred)
         keychain = Keychain(seed, coin_decred.curve_name, ns)
-        approver = BasicApprover(tx, coin_decred)
-        signer = decred.Decred(tx, keychain, coin_decred, approver).signer()
+        signer = decred.Decred(tx, keychain, coin_decred, None).signer()
 
         for request, response in chunks(messages, 2):
             res = signer.send(request)
@@ -353,8 +351,7 @@ class TestSignTxDecred(unittest.TestCase):
         )
         ns = get_schemas_for_coin(coin_decred)
         keychain = Keychain(seed, coin_decred.curve_name, ns)
-        approver = BasicApprover(tx, coin_decred)
-        signer = decred.Decred(tx, keychain, coin_decred, approver).signer()
+        signer = decred.Decred(tx, keychain, coin_decred, None).signer()
 
         for request, response in chunks(messages, 2):
             res = signer.send(request)
diff --git a/core/tests/test_apps.bitcoin.signtx_grs.py b/core/tests/test_apps.bitcoin.signtx_grs.py
index d7ec509e6..53d519997 100644
--- a/core/tests/test_apps.bitcoin.signtx_grs.py
+++ b/core/tests/test_apps.bitcoin.signtx_grs.py
@@ -28,7 +28,6 @@ from apps.common import coins
 from apps.common.keychain import Keychain
 from apps.bitcoin.keychain import get_schemas_for_coin
 from apps.bitcoin.sign_tx import bitcoinlike, helpers
-from apps.bitcoin.sign_tx.approvers import BasicApprover
 
 
 EMPTY_SERIALIZED = TxRequestSerializedType(serialized_tx=bytearray())
@@ -104,8 +103,7 @@ class TestSignTx_GRS(unittest.TestCase):
         seed = bip39.seed(' '.join(['all'] * 12), '')
         ns = get_schemas_for_coin(coin)
         keychain = Keychain(seed, coin.curve_name, ns)
-        approver = BasicApprover(tx, coin)
-        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, approver).signer()
+        signer = bitcoinlike.Bitcoinlike(tx, keychain, coin, None).signer()
         for request, expected_response in chunks(messages, 2):
             response = signer.send(request)
             if isinstance(response, tuple):