diff --git a/electrum/exchange_rate.py b/electrum/exchange_rate.py
index ea0a79ca7..f3c67712d 100644
--- a/electrum/exchange_rate.py
+++ b/electrum/exchange_rate.py
@@ -567,6 +567,9 @@ class FxThread(ThreadJob, EventListener):
             return text
         return text[:dp_loc] + util.DECIMAL_POINT + text[dp_loc+1:]
 
+    def ccy_precision(self, ccy=None) -> int:
+        return CCY_PRECISIONS.get(self.ccy if ccy is None else ccy, 2)
+
     async def run(self):
         while True:
             # every few minutes, refresh spot price
diff --git a/electrum/gui/qml/components/controls/BtcField.qml b/electrum/gui/qml/components/controls/BtcField.qml
index 3afeaa029..4414dd709 100644
--- a/electrum/gui/qml/components/controls/BtcField.qml
+++ b/electrum/gui/qml/components/controls/BtcField.qml
@@ -1,4 +1,4 @@
-import QtQuick 2.6
+import QtQuick 2.15
 import QtQuick.Controls 2.0
 
 import org.electrum 1.0
@@ -11,6 +11,10 @@ TextField {
     font.family: FixedFont
     placeholderText: qsTr('Amount')
     inputMethodHints: Qt.ImhDigitsOnly
+    validator: RegularExpressionValidator {
+        regularExpression: Config.btcAmountRegex
+    }
+
     property Amount textAsSats
     onTextChanged: {
         textAsSats = Config.unitsToSats(amount.text)
diff --git a/electrum/gui/qml/components/controls/FiatField.qml b/electrum/gui/qml/components/controls/FiatField.qml
index fff8150e0..47cb53694 100644
--- a/electrum/gui/qml/components/controls/FiatField.qml
+++ b/electrum/gui/qml/components/controls/FiatField.qml
@@ -1,4 +1,4 @@
-import QtQuick 2.6
+import QtQuick 2.15
 import QtQuick.Controls 2.0
 
 import org.electrum 1.0
@@ -11,6 +11,10 @@ TextField {
     font.family: FixedFont
     placeholderText: qsTr('Amount')
     inputMethodHints: Qt.ImhDigitsOnly
+    validator: RegularExpressionValidator {
+        regularExpression: Daemon.fx.fiatAmountRegex
+    }
+
     onTextChanged: {
         if (amountFiat.activeFocus)
             btcfield.text = text == ''
diff --git a/electrum/gui/qml/qeconfig.py b/electrum/gui/qml/qeconfig.py
index b71811c94..5f1735fa8 100644
--- a/electrum/gui/qml/qeconfig.py
+++ b/electrum/gui/qml/qeconfig.py
@@ -2,11 +2,11 @@ import copy
 from decimal import Decimal
 from typing import TYPE_CHECKING
 
-from PyQt5.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, QObject
+from PyQt5.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, QObject, QRegularExpression
 
 from electrum.i18n import set_language, languages
 from electrum.logging import get_logger
-from electrum.util import DECIMAL_POINT_DEFAULT, format_satoshis
+from electrum.util import DECIMAL_POINT_DEFAULT, base_unit_name_to_decimal_point
 from electrum.invoices import PR_DEFAULT_EXPIRATION_WHEN_CREATING
 
 from .qetypes import QEAmount
@@ -82,6 +82,15 @@ class QEConfig(AuthMixin, QObject):
         self.config.set_base_unit(unit)
         self.baseUnitChanged.emit()
 
+    @pyqtProperty('QRegularExpression', notify=baseUnitChanged)
+    def btcAmountRegex(self):
+        decimal_point = base_unit_name_to_decimal_point(self.config.get_base_unit())
+        exp = '[0-9]{0,8}'
+        if decimal_point:
+            exp += '\\.'
+            exp += '[0-9]{0,%d}' % decimal_point
+        return QRegularExpression(exp)
+
     thousandsSeparatorChanged = pyqtSignal()
     @pyqtProperty(bool, notify=thousandsSeparatorChanged)
     def thousandsSeparator(self):
diff --git a/electrum/gui/qml/qefx.py b/electrum/gui/qml/qefx.py
index ce69cc304..c742d990d 100644
--- a/electrum/gui/qml/qefx.py
+++ b/electrum/gui/qml/qefx.py
@@ -1,7 +1,7 @@
 from datetime import datetime
 from decimal import Decimal
 
-from PyQt5.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, QObject
+from PyQt5.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, QObject, QRegularExpression
 
 from electrum.bitcoin import COIN
 from electrum.exchange_rate import FxThread
@@ -60,6 +60,15 @@ class QEFX(QObject, QtEventListener):
             self.fiatCurrencyChanged.emit()
             self.rateSourcesChanged.emit()
 
+    @pyqtProperty('QRegularExpression', notify=fiatCurrencyChanged)
+    def fiatAmountRegex(self):
+        decimals = self.fx.ccy_precision()
+        exp = '[0-9]*'
+        if decimals:
+            exp += '\\.'
+            exp += '[0-9]{0,%d}' % decimals
+        return QRegularExpression(exp)
+
     historicRatesChanged = pyqtSignal()
     @pyqtProperty(bool, notify=historicRatesChanged)
     def historicRates(self):