diff --git a/ocaml/TaskServer.ml b/ocaml/TaskServer.ml
index 1b2acdee..91fbd231 100644
--- a/ocaml/TaskServer.ml
+++ b/ocaml/TaskServer.ml
@@ -49,7 +49,7 @@ let zmq_context =
   ZMQ.Context.create ()
 
 let () =
-  ZMQ.Context.set_io_threads zmq_context 2
+  ZMQ.Context.set_io_threads zmq_context 8
 
 
 let bind_socket ~socket_type ~socket ~port =
diff --git a/src/Determinants/spindeterminants.irp.f b/src/Determinants/spindeterminants.irp.f
index bf753704..39efb26c 100644
--- a/src/Determinants/spindeterminants.irp.f
+++ b/src/Determinants/spindeterminants.irp.f
@@ -416,7 +416,7 @@ BEGIN_PROVIDER  [ double precision, psi_bilinear_matrix_values, (N_det,N_states)
 
     j = get_index_in_psi_det_beta_unique (psi_det(1,2,k),N_int)
     ASSERT (j>0)
-    ASSERT (j<=N_det_alpha_unique)
+    ASSERT (j<=N_det_beta_unique)
 
     do l=1,N_states
       psi_bilinear_matrix_values(k,l) = psi_coef(k,l)