diff --git a/src/determinants/configurations.irp.f b/src/determinants/configurations.irp.f
index c703a866..f4c22440 100644
--- a/src/determinants/configurations.irp.f
+++ b/src/determinants/configurations.irp.f
@@ -286,7 +286,7 @@ end
  enddo
 
 !- Check
-!  print *,  'Checking for duplicates in occ pattern'
+!  print *,  'Checking for duplicates in configuration'
 !  do i=1,N_configuration
 !   do j=i+1,N_configuration
 !     duplicate(1) = .True.
@@ -313,6 +313,29 @@ end
 
 END_PROVIDER
 
+BEGIN_PROVIDER [ integer, cfg_seniority_index, (0:elec_num) ]
+ implicit none
+ BEGIN_DOC
+ ! Returns the index in psi_configuration of the first cfg with
+ ! the requested seniority
+ END_DOC
+ integer :: i, k, s, sold
+ cfg_seniority_index(:) = -1
+ sold = -1
+ do i=1,N_configuration
+   s = 0
+   do k=1,N_int
+     if (psi_configuration(k,1,i) == 0_bit_kind) cycle
+     s = s + popcnt(psi_configuration(k,1,i))
+   enddo
+   if (s /= sold) then
+     sold = s
+     cfg_seniority_index(s) = i
+   endif
+ enddo
+END_PROVIDER
+
+
 BEGIN_PROVIDER [ integer, det_to_configuration, (N_det) ]
  implicit none
  BEGIN_DOC
diff --git a/src/determinants/connected_to_ref.irp.f b/src/determinants/connected_to_ref.irp.f
index a174659c..7b8ea3e4 100644
--- a/src/determinants/connected_to_ref.irp.f
+++ b/src/determinants/connected_to_ref.irp.f
@@ -12,17 +12,34 @@ integer*8 function det_search_key(det,Nint)
 end
 
 
-integer*8 function configuration_search_key(det,Nint)
+integer*8 function configuration_search_key(cfg,Nint)
   use bitmasks
   implicit none
   BEGIN_DOC
-! Return an integer*8 corresponding to a determinant index for searching
+  ! Returns an integer*8 corresponding to a determinant index for searching.
+  ! The left-most 8 bits contain the number of open shells+1. This ensures that the CSF
+  ! are packed with the same seniority.
   END_DOC
   integer, intent(in) :: Nint
-  integer(bit_kind), intent(in) :: det(Nint,2)
-  integer :: i
+  integer(bit_kind), intent(in) :: cfg(Nint,2)
+  integer :: i, n_open_shells
+  integer*8 :: mask
+
   i = shiftr(elec_alpha_num, bit_kind_shift)+1
-  configuration_search_key = int(shiftr(ior(det(i,1),det(i,2)),1)+sum(det),8)
+  configuration_search_key = int(shiftr(ior(cfg(i,1),cfg(i,2)),1)+sum(cfg),8)
+
+  mask = X'00FFFFFFFFFFFFFF'
+  configuration_search_key = iand(mask,configuration_search_key)
+
+  n_open_shells = 1
+  do i=1,Nint
+    if (cfg(i,1) == 0_bit_kind) cycle
+    n_open_shells = n_open_shells + popcnt(cfg(i,1))
+  enddo
+  mask = n_open_shells
+  mask = shiftl(mask,56)
+  configuration_search_key = ior (mask,configuration_search_key)
+
 end
 
 
diff --git a/src/zmq/utils.irp.f b/src/zmq/utils.irp.f
index 07e3a88f..c050e2cb 100644
--- a/src/zmq/utils.irp.f
+++ b/src/zmq/utils.irp.f
@@ -907,6 +907,10 @@ integer function get_task_from_taskserver(zmq_to_qp_run_socket,worker_id,task_id
 
   message = repeat(' ',512)
   rc = f77_zmq_recv(zmq_to_qp_run_socket, message, 1024, 0)
+  if (rc <= 0) then
+     print *, rc
+     stop "rc"
+  end if
   rc = min(1024,rc)
   read(message(1:rc),*, end=10, err=10) reply
   if (trim(reply) == 'get_task_reply') then