diff --git a/interface/ri_oper.py b/interface/ri_oper.py
index 770739a..a1191ca 100644
--- a/interface/ri_oper.py
+++ b/interface/ri_oper.py
@@ -20,6 +20,7 @@ import ri_data
 import ri_dep
 import os
 import subprocess
+import signal
 
 display_operation = None
 display_sub_operation = None