diff --git a/Detector/DetSegmentation/DetSegmentation/GridDriftChamber.h b/Detector/DetSegmentation/DetSegmentation/GridDriftChamber.h
index 38e236c0d19d8b4419184510036b9db7e873e261..ff4af90e5d584ee4dbb3c6b7b1b04c27c00aa9d8 100644
--- a/Detector/DetSegmentation/DetSegmentation/GridDriftChamber.h
+++ b/Detector/DetSegmentation/DetSegmentation/GridDriftChamber.h
@@ -70,9 +70,9 @@ public:
     updateParams(layer);
     for (int i = 0; i<numWires; ++i) {
 
-      double phi0 = m_offset;
+      phi0 = m_offset;
 
-      auto phi_start = _currentLayerphi * i + phi0;
+      auto phi_start = _currentLayerphi * (i+0.5) + phi0;
       auto phi_end = phi_start + _currentLayerphi;
 
       TVector3 Wstart = returnWirePosition(phi_start, 1);