diff --git a/src/qt/paymentserver.cpp b/src/qt/paymentserver.cpp
index ba5c06064..cfa87c16b 100644
--- a/src/qt/paymentserver.cpp
+++ b/src/qt/paymentserver.cpp
@@ -548,6 +548,7 @@ void PaymentServer::fetchPaymentACK(CWallet* wallet, SendCoinsRecipient recipien
     else {
         CPubKey newKey;
         if (wallet->GetKeyFromPool(newKey)) {
+            LOCK(wallet->cs_wallet); // SetAddressBook
             CKeyID keyID = newKey.GetID();
             wallet->SetAddressBook(keyID, strAccount, "refund");