diff --git a/filter/filter.c b/filter/filter.c
index 2a626188..fd2c16b1 100644
--- a/filter/filter.c
+++ b/filter/filter.c
@@ -112,7 +112,7 @@ static struct tbf rl_runtime_err = TBF_DEFAULT_LOG_LIMITS;
  * TWOARGS macro to get both of them evaluated.
  */
 static enum filter_return
-interpret(struct filter_state *fs, const struct f_line *line, uint argc, const struct f_val *argv, struct f_val *val)
+interpret(struct filter_state *fs, const struct f_line *line, uint argc, const struct f_val *argv, uint resc, struct f_val *resv)
 {
   /* Check of appropriate number of arguments */
   ASSERT(line->args == argc);
@@ -178,21 +178,14 @@ interpret(struct filter_state *fs, const struct f_line *line, uint argc, const s
     fstk->ecnt--;
   }
 
-  if (fstk->vcnt == 0) {
-    if (val) {
-      log_rl(&rl_runtime_err, L_ERR "filters: No value left on stack");
-      return F_ERROR;
-    }
-    return F_NOP;
+  if (fstk->vcnt != resc)
+  {
+    log_rl(&rl_runtime_err, L_ERR "Filter expected to leave %d values on stack but %d left instead", resc, fstk->vcnt);
+    return F_ERROR;
   }
 
-  if (val && (fstk->vcnt == 1)) {
-    *val = fstk->vstk[0];
-    return F_NOP;
-  }
-
-  log_rl(&rl_runtime_err, L_ERR "Too many items left on stack: %u", fstk->vcnt);
-  return F_ERROR;
+  memcpy(resv, fstk->vstk, sizeof(struct f_val) * resc);
+  return F_NOP;
 }
 
 
@@ -232,7 +225,7 @@ f_run_args(const struct filter *filter, struct rte *rte, uint argc, const struct
   f_stack_init(filter_state);
 
   /* Run the interpreter itself */
-  enum filter_return fret = interpret(&filter_state, filter->root, argc, argv, NULL);
+  enum filter_return fret = interpret(&filter_state, filter->root, argc, argv, 0, NULL);
 
   /* Process the filter output, log it and return */
   if (fret < F_ACCEPT) {
@@ -258,7 +251,7 @@ f_run_args(const struct filter *filter, struct rte *rte, uint argc, const struct
  */
 
 enum filter_return
-f_eval_rte(const struct f_line *expr, struct rte *rte, uint argc, const struct f_val *argv, struct f_val *pres)
+f_eval_rte(const struct f_line *expr, struct rte *rte, uint argc, const struct f_val *argv, uint resc, struct f_val *resv)
 {
   filter_state = (struct filter_state) {
     .rte = rte,
@@ -266,14 +259,14 @@ f_eval_rte(const struct f_line *expr, struct rte *rte, uint argc, const struct f
 
   f_stack_init(filter_state);
 
-  return interpret(&filter_state, expr, argc, argv, pres);
+  return interpret(&filter_state, expr, argc, argv, resc, resv);
 }
 
 /*
  * f_eval - get a value of a term
  * @expr: filter line containing the term
  * @tmp_pool: long data may get allocated from this pool
- * @pres: here the output will be stored
+ * @pres: here the output will be stored if requested
  */
 enum filter_return
 f_eval(const struct f_line *expr, struct f_val *pres)
@@ -282,7 +275,7 @@ f_eval(const struct f_line *expr, struct f_val *pres)
 
   f_stack_init(filter_state);
 
-  enum filter_return fret = interpret(&filter_state, expr, 0, NULL, pres);
+  enum filter_return fret = interpret(&filter_state, expr, 0, NULL, !!pres, pres);
   return fret;
 }
 
diff --git a/filter/filter.h b/filter/filter.h
index 121da468..8d495e2d 100644
--- a/filter/filter.h
+++ b/filter/filter.h
@@ -54,7 +54,7 @@ struct rte;
 
 enum filter_return f_run(const struct filter *filter, struct rte *rte, int flags);
 enum filter_return f_run_args(const struct filter *filter, struct rte *rte, uint argc, const struct f_val *argv, int flags);
-enum filter_return f_eval_rte(const struct f_line *expr, struct rte *rte, uint argc, const struct f_val *argv, struct f_val *pres);
+enum filter_return f_eval_rte(const struct f_line *expr, struct rte *rte, uint argc, const struct f_val *argv, uint resc, struct f_val *resv);
 enum filter_return f_eval_buf(const struct f_line *expr, buffer *buf);
 
 struct f_val cf_eval_tmp(const struct f_inst *inst, int type);
diff --git a/proto/static/static.c b/proto/static/static.c
index 27b9a26f..c43f098c 100644
--- a/proto/static/static.c
+++ b/proto/static/static.c
@@ -122,7 +122,7 @@ static_announce_rte(struct static_proto *p, struct static_route *r)
 
   /* Evaluate the filter */
   if (r->cmds)
-    f_eval_rte(r->cmds, e, 0, NULL, NULL);
+    f_eval_rte(r->cmds, e, 0, NULL, 0, NULL);
 
   rte_update(p->p.main_channel, r->net, e, src);
   static_free_source(src, r->index);