diff --git a/Geo/MZoneBoundary.h b/Geo/MZoneBoundary.h
index 48c837c47f634532be64c1e7c8c25a15d2a22843..12f4589e6329a90d061c78f0dd235cb94a33749b 100644
--- a/Geo/MZoneBoundary.h
+++ b/Geo/MZoneBoundary.h
@@ -34,7 +34,7 @@ struct ZonePair
   int zone2;
   ZonePair(const int _zone1, const int _zone2) 
   {
-    if(_zone1 < zone2) {
+    if(_zone1 < _zone2) {
       zone1 = _zone1;
       zone2 = _zone2;
     }