diff --git a/src/ffi_ZDC_HCAL.cpp b/src/ffi_ZDC_HCAL.cpp
index b8051b7530e7dc2ad141383adb443b4102aaa417..2332a9d18783ce1fa898edb071c676655b287050 100644
--- a/src/ffi_ZDC_HCAL.cpp
+++ b/src/ffi_ZDC_HCAL.cpp
@@ -36,6 +36,7 @@ static Ref_t createDetector(Detector& lcdd, xml_h e, SensitiveDetector sens) {
 	int layer_num = 1;
 	int slice_num = 1;
 	double totWidth = Layering(x_det).totalThickness();
+	totWidth += 2*13;
 	Box envelope (pixel_x/2.0, pixel_y/2.0, totWidth/2.0);
 	Volume envelopeVol(det_name+"_envelope", envelope, air); 
 	PlacedVolume pv;