diff --git a/src/interface/Interface_graphic.cpp b/src/interface/Interface_graphic.cpp
index 86e289a121d3b6da466d7faa5dcf7421935ce304..8b685bbc98b876860ec3381f010a529db59e6600 100644
--- a/src/interface/Interface_graphic.cpp
+++ b/src/interface/Interface_graphic.cpp
@@ -772,10 +772,14 @@ void Interface_graphic::on_close_triggered(){
 
 void Interface_graphic::on_quit_triggered(){
 
-    ((QWidget*)_ui_node_selection)->close();
-    ((QWidget*)_ui_interval_selection)->close();
-    ((QWidget*)_ui_help_window)->close();
-    ((QWidget*)_ui_info_window)->close();
+    if( NULL != _ui_node_selection)
+        ((QWidget*)_ui_node_selection)->close();
+    if( NULL != _ui_interval_selection)
+        ((QWidget*)_ui_interval_selection)->close();
+    if( NULL != _ui_help_window)
+        ((QWidget*)_ui_help_window)->close();
+    if( NULL != _ui_info_window)
+        ((QWidget*)_ui_info_window)->close();
     ((QWidget*)this)->close();
 }