diff --git a/test/fracviewer.cxx b/test/fracviewer.cxx
index bc45cc045..e19fd568c 100644
--- a/test/fracviewer.cxx
+++ b/test/fracviewer.cxx
@@ -331,6 +331,7 @@ void agvSwitchMoveMode(int move)
 
 void agvHandleButton(int button, int state, int x, int y)
 {
+ if (button > GLUT_RIGHT_BUTTON)return;
  if (state == GLUT_DOWN && downb == -1) {  
     lastx = downx = x;
     lasty = downy = y;