diff --git a/src/apps/common/signtx.py b/src/apps/common/signtx.py
index 32365b19d9..f6ddffe857 100644
--- a/src/apps/common/signtx.py
+++ b/src/apps/common/signtx.py
@@ -39,6 +39,13 @@ class UiConfirmTotal:
         self.coin = coin
 
 
+class UiConfirmFeeOverThreshold:
+
+    def __init__(self, fee: int, coin: CoinType):
+        self.fee = fee
+        self.coin = coin
+
+
 def confirm_output(output: TxOutputType, coin: CoinType):
     return (yield UiConfirmOutput(output, coin))
 
@@ -47,6 +54,10 @@ def confirm_total(spending: int, fee: int, coin: CoinType):
     return (yield UiConfirmTotal(spending, fee, coin))
 
 
+def confirm_feeoverthreshold(fee: int, coin: CoinType):
+    return (yield UiConfirmFeeOverThreshold(fee, coin))
+
+
 def request_tx_meta(tx_req: TxRequest, tx_hash: bytes=None):
     tx_req.request_type = TXMETA
     tx_req.details.tx_hash = tx_hash
@@ -83,6 +94,8 @@ def request_tx_finish(tx_req: TxRequest):
     yield tx_req
     tx_req.serialized = None
 
+def estimate_tx_size(inputs, outputs):
+    return 10 + inputs * 149 + outputs * 35
 
 # Transaction signing
 # ===
@@ -145,6 +158,12 @@ async def sign_tx(tx: SignTx, root):
         raise SigningError(FailureType.NotEnoughFunds,
                            'Not enough funds')
 
+    if fee > coin.maxfee_kb * ((estimate_tx_size(tx_inputs_count, tx_outputs_count) + 999) // 1000):
+        if not await confirm_feeoverthreshold(fee, coin):
+            raise SigningError(FailureType.ActionCancelled,
+                               'Signing cancelled')
+
+
     if not await confirm_total(total_out - change_out, fee, coin):
         raise SigningError(FailureType.ActionCancelled,
                            'Total cancelled')
diff --git a/src/apps/wallet/__init__.py b/src/apps/wallet/__init__.py
index 1830db5c8d..e1f07e09f4 100644
--- a/src/apps/wallet/__init__.py
+++ b/src/apps/wallet/__init__.py
@@ -25,8 +25,9 @@ def dispatch_SignTx(*args, **kwargs):
 @unimport
 async def dispatch_EstimateTxSize(msg, session_id):
     from trezor.messages.TxSize import TxSize
+    from ..common.signtx import estimate_tx_size
     m = TxSize()
-    m.tx_size =  10 + msg.inputs_count * 149 + msg.outputs_count * 35
+    m.tx_size = estimate_tx_size(msg.inputs_count, msg.outputs_count)
     return m
 
 
diff --git a/src/apps/wallet/layout_sign_tx.py b/src/apps/wallet/layout_sign_tx.py
index 9f525e5b6c..43a13602c8 100644
--- a/src/apps/wallet/layout_sign_tx.py
+++ b/src/apps/wallet/layout_sign_tx.py
@@ -32,7 +32,18 @@ async def confirm_total(session_id, spending, fee, coin):
     return await hold_to_confirm(session_id, content, SignTx)
 
 
-# @unimport
+async def confirm_feeoverthreshold(session_id, fee, coin):
+    from trezor import ui
+    from trezor.ui.text import Text
+    from trezor.messages.ButtonRequestType import FeeOverThreshold
+    from ..common.confirm import confirm
+
+    content = Text('Confirm high fee:', ui.ICON_RESET,
+                   ui.BOLD, format_amount(fee, coin))
+    return await confirm(session_id, content, FeeOverThreshold)
+
+
+@unimport
 async def layout_sign_tx(message, session_id):
     from ..common.seed import get_root_node
     from ..common import signtx
@@ -50,14 +61,16 @@ async def layout_sign_tx(message, session_id):
             req = signer.send(res)
         except signtx.SigningError as e:
             raise wire.FailureError(*e.args)
-        if isinstance(req, TxRequest):
+        if req.__qualname__ == 'TxRequest':
             if req.request_type == RequestType.TXFINISHED:
                 break
             res = await wire.reply_message(session_id, req, TxAck)
-        elif isinstance(req, signtx.UiConfirmOutput):
+        elif req.__qualname__ == 'UiConfirmOutput':
             res = await confirm_output(session_id, req.output, req.coin)
-        elif isinstance(req, signtx.UiConfirmTotal):
+        elif req.__qualname__ == 'UiConfirmTotal':
             res = await confirm_total(session_id, req.spending, req.fee, req.coin)
-        else:
+        elif req.__qualname__ == 'UiConfirmFeeOverThreshold':
+            res = await confirm_feeoverthreshold(session_id, req.fee, req.coin)
+    else:
             raise ValueError('Invalid signing instruction')
     return req