diff --git a/stable/champ/write_champ_csf.irp.f b/stable/champ/write_champ_csf.irp.f
index 580436f..af43435 100644
--- a/stable/champ/write_champ_csf.irp.f
+++ b/stable/champ/write_champ_csf.irp.f
@@ -1,16 +1,17 @@
 subroutine write_champ_csf
   implicit none
 
-  integer, parameter             :: iunit=12, istate=1
+  integer, parameter             :: istate=1
   character*(2048)               :: format
   integer                        :: i, n_elements, j, k
   integer, allocatable           :: list(:,:)
 
-  integer                        :: startdet, enddet
+  integer                        :: startdet, enddet, iunit
   integer                        :: ndetI, bfIcfg, s
   double precision               :: phasedet
   integer                        :: idx
 
+  open(newunit=iunit, file='det.'//ezfio_filename)
 
   write(iunit, '(A, X, I4,  X, A, X, I4)') '&electrons nelec', elec_num, 'nup', elec_alpha_num