diff --git a/gui/qt/main_window.py b/gui/qt/main_window.py
index f9dd8cbf..32a57bfc 100644
--- a/gui/qt/main_window.py
+++ b/gui/qt/main_window.py
@@ -251,6 +251,9 @@ class ElectrumWindow(QMainWindow):
             except Exception as e:
                 traceback.print_exc(file=sys.stdout)
                 self.show_message(str(e))
+        # call synchronize to regenerate addresses in case we are offline
+        if self.wallet.get_master_public_keys() and self.wallet.addresses() == []:
+            self.wallet.synchronize()
 
 
     def open_wallet(self):
diff --git a/lib/wallet.py b/lib/wallet.py
index 2063be31..b576ba19 100644
--- a/lib/wallet.py
+++ b/lib/wallet.py
@@ -1203,8 +1203,9 @@ class Deterministic_Wallet(Abstract_Wallet):
         self.save_accounts()
 
     def synchronize(self):
-        for account in self.accounts.values():
-            account.synchronize(self)
+        with self.lock:
+            for account in self.accounts.values():
+                account.synchronize(self)
 
     def restore(self, callback):
         from i18n import _