diff --git a/examples/iguana_ex_fortran_01_action_functions.f b/examples/iguana_ex_fortran_01_action_functions.f
index c019aaeb..288e21c2 100644
--- a/examples/iguana_ex_fortran_01_action_functions.f
+++ b/examples/iguana_ex_fortran_01_action_functions.f
@@ -45,11 +45,13 @@ program iguana_ex_fortran_01_action_functions
       integer(c_int) stat(N_MAX)
       integer(c_int) sector(N_MAX)
       real(c_float)  torus(N_MAX)
+      integer(c_int) runnum(N_MAX)
 
 c     iguana algorithm outputs
       logical(c_bool) accept(N_MAX)  ! filter
       real(c_double) qx, qy, qz, qE  ! q vector
       real(c_double) Q2, x, y, W, nu ! inclusive kinematics
+      integer(c_int) key_vz_filter   ! key for Z-vertex filter
 
 c     iguana algorithm indices
       integer(c_int) algo_eb_filter, algo_vz_filter,
@@ -180,6 +182,13 @@ program iguana_ex_fortran_01_action_functions
         call hipo_read_float('REC::Particle', 'vz', nr, vz, N_MAX)
         call hipo_read_int('REC::Particle', 'status', nr, stat, N_MAX)
         call hipo_read_float('RUN::config', 'torus', nr, torus, N_MAX)
+        call hipo_read_int('RUN::config', 'run', nr, runnum, N_MAX)
+
+c       before using the Z-vertext filter, we must "prepare" the
+c       algorithm's configuration for this event; the resulting
+c       'key_vz_filter' must be passed to the action function
+        call iguana_clas12_zvertexfilter_prepareevent(
+     &      algo_vz_filter, runnum(1), key_vz_filter)
 
 c       call iguana filters
 c       - the `logical` variable `accept` must be initialized to
@@ -193,7 +202,8 @@ program iguana_ex_fortran_01_action_functions
           call iguana_clas12_eventbuilderfilter_filter(
      &      algo_eb_filter, pid(i), accept(i))
           call iguana_clas12_zvertexfilter_filter(
-     &      algo_vz_filter, vz(i), pid(i), stat(i), accept(i))
+     &      algo_vz_filter, vz(i), pid(i), stat(i),
+     &      key_vz_filter, accept(i))
           print *, '  i = ', i, '  pid = ', pid(i), ' vz = ', vz(i),
      &      '  status = ', stat(i), '  =>  accept = ', accept(i)
         enddo
diff --git a/src/iguana/algorithms/clas12/ZVertexFilter/Action.yaml b/src/iguana/algorithms/clas12/ZVertexFilter/Action.yaml
index 691add97..ad1d2061 100644
--- a/src/iguana/algorithms/clas12/ZVertexFilter/Action.yaml
+++ b/src/iguana/algorithms/clas12/ZVertexFilter/Action.yaml
@@ -2,6 +2,14 @@ algorithm:
   name: 'clas12::ZVertexFilter'
 
 actions:
+  - name: PrepareEvent
+    type: creator
+    inputs:
+      - name: runnum
+        type: int
+    outputs:
+      - type: concurrent_key_t
+        cast: int
   - name: Filter
     type: filter
     inputs: