diff --git a/src/SiTrackerEndcap_geo.cpp b/src/SiTrackerEndcap_geo.cpp
index 4e91b7e48a7ec5059faaf5e28f740536afaee51e..59c914013b365c2640ea70f6926b4f13ec951398 100644
--- a/src/SiTrackerEndcap_geo.cpp
+++ b/src/SiTrackerEndcap_geo.cpp
@@ -193,7 +193,12 @@ static Ref_t create_detector(Detector& description, xml_h e, SensitiveDetector s
       ++ring_num;
     }
   }
-  pv = motherVol.placeVolume(assembly);
+  // hack to get around the way ACTS defines pos/neg endcaps based on zposition 
+  Position final_pos(0,0,0);
+  if(reflect) {
+    final_pos = Position(0,0,-1.0e-9);
+  }
+  pv = motherVol.placeVolume(assembly,final_pos);
   pv.addPhysVolID("system",det_id);
   sdet.setPlacement(pv);
   return sdet;