diff --git a/source/geometries/Next100SiPMBoard.cc b/source/geometries/Next100SiPMBoard.cc
index a4ff992ac..49968b2b3 100644
--- a/source/geometries/Next100SiPMBoard.cc
+++ b/source/geometries/Next100SiPMBoard.cc
@@ -162,7 +162,7 @@ void Next100SiPMBoard::Construct()
   G4double mask_hole_length = mask_thickness_ - wls_thickness;
   G4double mask_hole_zpos   = - mask_thickness_/2. + mask_hole_length/2.;
   G4double mask_hole_x = 6.0 * mm;
-  G4double mask_hole_y = 5.0 * mm;
+  G4double mask_hole_y = 6.0 * mm;
 
   G4Box* mask_hole_solid_vol =
     new G4Box(mask_hole_name, mask_hole_x/2., mask_hole_y/2., mask_hole_length/2.);