diff --git a/gui/qt/main_window.py b/gui/qt/main_window.py
index fcd149d93..3aea8737e 100644
--- a/gui/qt/main_window.py
+++ b/gui/qt/main_window.py
@@ -52,7 +52,7 @@ from electrum.util import (block_explorer, block_explorer_info, format_time,
 from electrum import Transaction, mnemonic
 from electrum import util, bitcoin, commands, coinchooser
 from electrum import SimpleConfig, paymentrequest
-from electrum.wallet import Wallet, Multisig_Wallet
+from electrum.wallet import Wallet, Multisig_Wallet, P2PK_Wallet
 
 from amountedit import BTCAmountEdit, MyLineEdit, BTCkBEdit
 from network_dialog import NetworkDialog
@@ -1758,20 +1758,35 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
 
     @protected
     def do_sign(self, address, message, signature, password):
-        message = unicode(message.toPlainText()).encode('utf-8')
-        task = partial(self.wallet.sign_message, str(address.text()),
-                       message, password)
+        address  = str(address.text()).strip()
+        message = unicode(message.toPlainText()).encode('utf-8').strip()
+        if not bitcoin.is_address(address):
+            self.show_message('Invalid Bitcoin address.')
+            return
+        if not bitcoin.is_p2pkh(address):
+            self.show_message('Cannot sign messages with this type of address.')
+            return
+        if not wallet.is_mine(address):
+            self.show_message('Address not in wallet.')
+            return
+        task = partial(self.wallet.sign_message, address, message, password)
         def show_signed_message(sig):
             signature.setText(base64.b64encode(sig))
         self.wallet.thread.add(task, on_success=show_signed_message)
 
     def do_verify(self, address, message, signature):
-        message = unicode(message.toPlainText())
-        message = message.encode('utf-8')
+        address  = str(address.text()).strip()
+        message = unicode(message.toPlainText()).encode('utf-8').strip()
+        if not bitcoin.is_address(address):
+            self.show_message('Invalid Bitcoin address.')
+            return
+        if not bitcoin.is_p2pkh(address):
+            self.show_message('Cannot verify messages with this type of address.')
+            return
         try:
             # This can throw on invalid base64
             sig = base64.b64decode(str(signature.toPlainText()))
-            verified = bitcoin.verify_message(address.text(), sig, message)
+            verified = bitcoin.verify_message(address, sig, message)
         except:
             verified = False
         if verified:
diff --git a/lib/bitcoin.py b/lib/bitcoin.py
index 050fa4938..07a102a1a 100644
--- a/lib/bitcoin.py
+++ b/lib/bitcoin.py
@@ -384,6 +384,15 @@ def is_address(addr):
         return False
     return addr == hash_160_to_bc_address(h, addrtype)
 
+def is_p2pkh(addr):
+    if is_address(addr):
+        addrtype, h = bc_address_to_hash_160(addr)
+        return addrtype in [0]
+
+def is_p2sh(addr):
+    if is_address(addr):
+        addrtype, h = bc_address_to_hash_160(addr)
+        return addrtype in [5]
 
 def is_private_key(key):
     try: