diff --git a/package.json b/package.json
index 5bc89e4..3ed3445 100644
--- a/package.json
+++ b/package.json
@@ -14,7 +14,7 @@
     "DIST_FOLDER": "../bitgesell-wallet-dist"
   },
   "scripts": {
-    "test": "eslint 'src/*.js'",
+    "test": "eslint 'src/**/*.js' && node test/send_preflight_test.js",
     "local-server": "IP=$npm_package_config_IP PORT=$npm_package_config_PORT node local-server.js",
     "start": "npm test && npm run local-server",
     "build": "./build.sh $npm_package_config_DIST_FOLDER",
diff --git a/src/send/send.js b/src/send/send.js
index bdb74de..9b4532c 100644
--- a/src/send/send.js
+++ b/src/send/send.js
@@ -181,7 +181,13 @@ const sendFormInit = () => {
 };
 
 const send = () => {
-	if ($send.querySelector('.is-invalid')) return;
+	if (!isAddressValid($sendToVal.value)) {
+		$sendToVal.classList.remove('is-valid');
+		$sendToVal.classList.add('is-invalid');
+		return;
+	}
+	calcAmountSpent();
+	if ($send.querySelector('.is-invalid') || !newTx) return;
 	$send.querySelector('fieldset').setAttribute('disabled', '');
 	const url = new URL(localStorage.nodeAddress);
 	const fetchParams = {
diff --git a/test/send_preflight_test.js b/test/send_preflight_test.js
new file mode 100644
index 0000000..1b4c74c
--- /dev/null
+++ b/test/send_preflight_test.js
@@ -0,0 +1,139 @@
+const assert = require('assert');
+const fs = require('fs');
+const vm = require('vm');
+
+function makeClassList() {
+	const values = new Set();
+	return {
+		add: (...names) => names.forEach((name) => values.add(name)),
+		remove: (...names) => names.forEach((name) => values.delete(name)),
+		contains: (name) => values.has(name),
+	};
+}
+
+function input(value = '') {
+	return {
+		value,
+		classList: makeClassList(),
+		addEventListener: () => {},
+	};
+}
+
+function spanBox() {
+	return {
+		innerHTML: '',
+		querySelector: () => ({innerText: ''}),
+	};
+}
+
+function buildContext() {
+	const fieldset = {
+		disabled: false,
+		setAttribute: (name) => {
+			if (name === 'disabled') fieldset.disabled = true;
+		},
+		removeAttribute: (name) => {
+			if (name === 'disabled') fieldset.disabled = false;
+		},
+	};
+	const sendRoot = {
+		querySelector: (selector) => {
+			if (selector === 'fieldset') return fieldset;
+			if (selector === '.is-invalid') {
+				return context.$sendToVal.classList.contains('is-invalid') ||
+					context.$sendAmountVal.classList.contains('is-invalid') ? {} : null;
+			}
+			return {addEventListener: () => {}, reset: () => {}};
+		},
+	};
+	let fetchCalls = 0;
+	let lastFetchParams;
+	const context = {
+		console,
+		URL,
+		btoa: (value) => Buffer.from(value).toString('base64'),
+		document: {addEventListener: () => {}},
+		window: {location: {hash: ''}, scrollTo: () => {}},
+		localStorage: {nodeAddress: 'http://rpc-user:rpc-pass@127.0.0.1:8332'},
+		storage: {addresses: {fromAddress: {private: 'priv', balance: 1000, input_count: 0}}},
+		coinPrice: {price: 1},
+		sb: {
+			toSatoshi: (value) => Math.round(Number(value) * 100),
+			toBitcoin: (value) => String(value / 100),
+		},
+		Transaction: function Transaction() {},
+		Option: function Option(text, value) { this.text = text; this.value = value; },
+		Swal: {fire: () => ({then: () => {}})},
+		initHtmlElements: () => {},
+		formHandler: () => {},
+		show: () => {},
+		hide: () => {},
+		getAddressUtxo: () => {},
+		getBalanceSum: () => {},
+		saveToCryptoStorage: () => {},
+		fetchQuery: (url, onSuccess, params) => {
+			fetchCalls++;
+			lastFetchParams = {url, params};
+			onSuccess({result: 'txid'});
+		},
+		isAddressValid: (value) => value === 'validAddress',
+		$sendFromVal: input('fromAddress'),
+		$sendBalance: spanBox(),
+		$sendToVal: input('validAddress'),
+		$sendAmountVal: input('1'),
+		$sendAmountMax: {addEventListener: () => {}},
+		$sendAmountPrice: spanBox(),
+		$sendFeeVal: input('0.1'),
+		$sendFormBtn: {innerHTML: ''},
+		$sendNewBalance: spanBox(),
+		$send: sendRoot,
+		$welcome: {},
+		$dashboard: {},
+		$myAddresses: {},
+		$newAddress: {},
+		$transactions: {},
+		$setPassword: {},
+		$mobileMenu: {},
+		$main: {},
+	};
+	Object.defineProperties(context, {
+		fetchCalls: {get: () => fetchCalls},
+		lastFetchParams: {get: () => lastFetchParams},
+		fieldset: {get: () => fieldset},
+	});
+	return context;
+}
+
+const source = fs.readFileSync('src/send/send.js', 'utf8');
+const assertions = `
+(function runSendPreflightAssertions() {
+	$sendToVal.value = 'invalidAddress';
+	send();
+	assert.strictEqual(fetchCalls, 0, 'invalid recipient must not call sendrawtransaction');
+	assert.strictEqual($sendToVal.classList.contains('is-invalid'), true, 'invalid recipient is marked invalid at submit time');
+	assert.strictEqual(fieldset.disabled, false, 'invalid recipient must not disable the form');
+
+	$sendToVal.value = 'validAddress';
+	$sendToVal.classList.remove('is-invalid');
+	newTx = null;
+	sendParams = {fromAmount: 1000};
+	send();
+	assert.strictEqual(fetchCalls, 0, 'empty serialized transaction must not call sendrawtransaction');
+	assert.strictEqual(fieldset.disabled, false, 'empty transaction must not disable the form');
+
+	newTx = '01000000';
+	sendParams = {fromAmount: 1000};
+	send();
+	assert.strictEqual(fetchCalls, 1, 'valid preflight calls sendrawtransaction exactly once');
+	assert.strictEqual(fieldset.disabled, true, 'valid preflight disables the form while sending');
+	assert.strictEqual(lastFetchParams.url, 'http://127.0.0.1:8332');
+	assert.strictEqual(lastFetchParams.params.headers.Authorization, 'Basic cnBjLXVzZXI6cnBjLXBhc3M=');
+	assert.ok(lastFetchParams.params.body.includes('sendrawtransaction'), 'RPC body sends transaction');
+	assert.ok(lastFetchParams.params.body.includes('01000000'), 'RPC body includes serialized transaction');
+})();
+`;
+const context = buildContext();
+context.assert = assert;
+vm.createContext(context);
+vm.runInContext(source + assertions, context, {filename: 'send_preflight_vm.js'});
+console.log('send preflight tests passed');