diff --git a/include/proto/stick_table.h b/include/proto/stick_table.h
index 0c26fbe..57ca223 100644
--- a/include/proto/stick_table.h
+++ b/include/proto/stick_table.h
@@ -48,7 +48,7 @@
 struct stksess *stktable_update_key(struct stktable *table, struct stktable_key *key);
 struct stktable_key *stktable_fetch_key(struct stktable *t, struct proxy *px,
 				        struct session *l4, void *l7, unsigned int opt,
-				        struct sample_expr *expr);
+				        struct sample_expr *expr, struct sample *smp);
 int stktable_compatible_sample(struct sample_expr *expr, unsigned long table_type);
 int stktable_get_data_type(char *name);
 struct proxy *find_stktable(const char *name);
diff --git a/src/proto_tcp.c b/src/proto_tcp.c
index 65c4fda..1aac0d9 100644
--- a/src/proto_tcp.c
+++ b/src/proto_tcp.c
@@ -1027,7 +1027,7 @@
 					continue;
 
 				t = rule->act_prm.trk_ctr.table.t;
-				key = stktable_fetch_key(t, s->be, s, &s->txn, SMP_OPT_DIR_REQ|SMP_OPT_FINAL, rule->act_prm.trk_ctr.expr);
+				key = stktable_fetch_key(t, s->be, s, &s->txn, SMP_OPT_DIR_REQ|SMP_OPT_FINAL, rule->act_prm.trk_ctr.expr, NULL);
 
 				if (key && (ts = stktable_get_entry(t, key))) {
 					session_track_stkctr(&s->stkctr[tcp_trk_idx(rule->action)], t, ts);
@@ -1228,7 +1228,7 @@
 					continue;
 
 				t = rule->act_prm.trk_ctr.table.t;
-				key = stktable_fetch_key(t, s->be, s, &s->txn, SMP_OPT_DIR_REQ|SMP_OPT_FINAL, rule->act_prm.trk_ctr.expr);
+				key = stktable_fetch_key(t, s->be, s, &s->txn, SMP_OPT_DIR_REQ|SMP_OPT_FINAL, rule->act_prm.trk_ctr.expr, NULL);
 
 				if (key && (ts = stktable_get_entry(t, key)))
 					session_track_stkctr(&s->stkctr[tcp_trk_idx(rule->action)], t, ts);
diff --git a/src/session.c b/src/session.c
index e26f5ad..df85170 100644
--- a/src/session.c
+++ b/src/session.c
@@ -1458,7 +1458,7 @@
 		if (ret) {
 			struct stktable_key *key;
 
-			key = stktable_fetch_key(rule->table.t, px, s, &s->txn, SMP_OPT_DIR_REQ|SMP_OPT_FINAL, rule->expr);
+			key = stktable_fetch_key(rule->table.t, px, s, &s->txn, SMP_OPT_DIR_REQ|SMP_OPT_FINAL, rule->expr, NULL);
 			if (!key)
 				continue;
 
@@ -1561,7 +1561,7 @@
 		if (ret) {
 			struct stktable_key *key;
 
-			key = stktable_fetch_key(rule->table.t, px, s, &s->txn, SMP_OPT_DIR_RES|SMP_OPT_FINAL, rule->expr);
+			key = stktable_fetch_key(rule->table.t, px, s, &s->txn, SMP_OPT_DIR_RES|SMP_OPT_FINAL, rule->expr, NULL);
 			if (!key)
 				continue;
 
diff --git a/src/stick_table.c b/src/stick_table.c
index c6463ec..a708d3c 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -601,15 +601,17 @@
  * Process a fetch + format conversion as defined by the sample expression <expr>
  * on request or response considering the <opt> parameter. Returns either NULL if
  * no key could be extracted, or a pointer to the converted result stored in
- * static_table_key in format <table_type>.
+ * static_table_key in format <table_type>. If <smp> is not NULL, it will be reset
+ * and its flags will be initialized so that the caller gets a copy of the input
+ * sample, and knows why it was not accepted (eg: SMP_F_MAY_CHANGE is present).
  */
 struct stktable_key *stktable_fetch_key(struct stktable *t, struct proxy *px, struct session *l4, void *l7,
-					unsigned int opt,
-                                        struct sample_expr *expr)
+                                        unsigned int opt, struct sample_expr *expr, struct sample *smp)
 {
-	struct sample *smp;
+	if (smp)
+		memset(smp, 0, sizeof(*smp));
 
-	smp = sample_process(px, l4, l7, opt, expr, NULL);
+	smp = sample_process(px, l4, l7, opt, expr, smp);
 	if (!smp)
 		return NULL;