diff --git a/ui.cpp b/ui.cpp
index ed5ccdea..a6f55005 100644
--- a/ui.cpp
+++ b/ui.cpp
@@ -1929,69 +1929,73 @@ void CSendDialog::OnButtonPaste(wxCommandEvent& event)
 
 void CSendDialog::OnButtonSend(wxCommandEvent& event)
 {
-    CWalletTx wtx;
-    string strAddress = (string)m_textCtrlAddress->GetValue();
-
-    // Parse amount
-    int64 nValue = 0;
-    if (!ParseMoney(m_textCtrlAmount->GetValue(), nValue) || nValue <= 0)
-    {
-        wxMessageBox(_("Error in amount  "), _("Send Coins"));
-        return;
-    }
-    if (nValue > GetBalance())
+    static CCriticalSection cs_sendlock;
+    TRY_CRITICAL_BLOCK(cs_sendlock)
     {
-        wxMessageBox(_("Amount exceeds your balance  "), _("Send Coins"));
-        return;
-    }
-    if (nValue + nTransactionFee > GetBalance())
-    {
-        wxMessageBox(string(_("Total exceeds your balance when the ")) + FormatMoney(nTransactionFee) + _(" transaction fee is included  "), _("Send Coins"));
-        return;
-    }
+        CWalletTx wtx;
+        string strAddress = (string)m_textCtrlAddress->GetValue();
 
-    // Parse bitcoin address
-    uint160 hash160;
-    bool fBitcoinAddress = AddressToHash160(strAddress, hash160);
+        // Parse amount
+        int64 nValue = 0;
+        if (!ParseMoney(m_textCtrlAmount->GetValue(), nValue) || nValue <= 0)
+        {
+            wxMessageBox(_("Error in amount  "), _("Send Coins"));
+            return;
+        }
+        if (nValue > GetBalance())
+        {
+            wxMessageBox(_("Amount exceeds your balance  "), _("Send Coins"));
+            return;
+        }
+        if (nValue + nTransactionFee > GetBalance())
+        {
+            wxMessageBox(string(_("Total exceeds your balance when the ")) + FormatMoney(nTransactionFee) + _(" transaction fee is included  "), _("Send Coins"));
+            return;
+        }
 
-    if (fBitcoinAddress)
-    {
-        // Send to bitcoin address
-        CScript scriptPubKey;
-        scriptPubKey << OP_DUP << OP_HASH160 << hash160 << OP_EQUALVERIFY << OP_CHECKSIG;
+        // Parse bitcoin address
+        uint160 hash160;
+        bool fBitcoinAddress = AddressToHash160(strAddress, hash160);
 
-        string strError = SendMoney(scriptPubKey, nValue, wtx, true);
-        if (strError == "")
-            wxMessageBox(_("Payment sent  "), _("Sending..."));
-        else if (strError != "ABORTED")
-            wxMessageBox(strError + "  ", _("Sending..."));
-    }
-    else
-    {
-        // Parse IP address
-        CAddress addr(strAddress);
-        if (!addr.IsValid())
+        if (fBitcoinAddress)
         {
-            wxMessageBox(_("Invalid address  "), _("Send Coins"));
-            return;
+            // Send to bitcoin address
+            CScript scriptPubKey;
+            scriptPubKey << OP_DUP << OP_HASH160 << hash160 << OP_EQUALVERIFY << OP_CHECKSIG;
+
+            string strError = SendMoney(scriptPubKey, nValue, wtx, true);
+            if (strError == "")
+                wxMessageBox(_("Payment sent  "), _("Sending..."));
+            else if (strError != "ABORTED")
+                wxMessageBox(strError + "  ", _("Sending..."));
         }
+        else
+        {
+            // Parse IP address
+            CAddress addr(strAddress);
+            if (!addr.IsValid())
+            {
+                wxMessageBox(_("Invalid address  "), _("Send Coins"));
+                return;
+            }
 
-        // Message
-        wtx.mapValue["to"] = strAddress;
-        wtx.mapValue["from"] = m_textCtrlFrom->GetValue();
-        wtx.mapValue["message"] = m_textCtrlMessage->GetValue();
+            // Message
+            wtx.mapValue["to"] = strAddress;
+            wtx.mapValue["from"] = m_textCtrlFrom->GetValue();
+            wtx.mapValue["message"] = m_textCtrlMessage->GetValue();
 
-        // Send to IP address
-        CSendingDialog* pdialog = new CSendingDialog(this, addr, nValue, wtx);
-        if (!pdialog->ShowModal())
-            return;
-    }
+            // Send to IP address
+            CSendingDialog* pdialog = new CSendingDialog(this, addr, nValue, wtx);
+            if (!pdialog->ShowModal())
+                return;
+        }
 
-    CRITICAL_BLOCK(cs_mapAddressBook)
-        if (!mapAddressBook.count(strAddress))
-            SetAddressBookName(strAddress, "");
+        CRITICAL_BLOCK(cs_mapAddressBook)
+            if (!mapAddressBook.count(strAddress))
+                SetAddressBookName(strAddress, "");
 
-    EndModal(true);
+        EndModal(true);
+    }
 }
 
 void CSendDialog::OnButtonCancel(wxCommandEvent& event)