diff --git a/gui/gui_classic.py b/gui/gui_classic.py
index a29e1cc2..2d4aa96c 100644
--- a/gui/gui_classic.py
+++ b/gui/gui_classic.py
@@ -33,7 +33,7 @@ from PyQt4.QtGui import *
 from PyQt4.QtCore import *
 import PyQt4.QtCore as QtCore
 
-from electrum.bitcoin import MIN_RELAY_TX_FEE
+from electrum.bitcoin import MIN_RELAY_TX_FEE, is_valid
 
 try:
     import icons_rc