diff --git a/include/re_hash.h b/include/re_hash.h
index 60494ad..873fa34 100644
--- a/include/re_hash.h
+++ b/include/re_hash.h
@@ -18,6 +18,7 @@ struct le *hash_apply(const struct hash *h, list_apply_h *ah, void *arg);
 struct list *hash_list(const struct hash *h, uint32_t key);
 uint32_t hash_bsize(const struct hash *h);
 void hash_flush(struct hash *h);
+void hash_clear(struct hash *h);
 uint32_t hash_valid_size(uint32_t size);
 
 
diff --git a/include/re_list.h b/include/re_list.h
index 1fd28a3..3045453 100644
--- a/include/re_list.h
+++ b/include/re_list.h
@@ -51,6 +51,7 @@ typedef bool (list_sort_h)(struct le *le1, struct le *le2, void *arg);
 
 void list_init(struct list *list);
 void list_flush(struct list *list);
+void list_clear(struct list *list);
 void list_append(struct list *list, struct le *le, void *data);
 void list_prepend(struct list *list, struct le *le, void *data);
 void list_insert_before(struct list *list, struct le *le, struct le *ile,
diff --git a/src/hash/hash.c b/src/hash/hash.c
index 82f13e6..45aa11e 100644
--- a/src/hash/hash.c
+++ b/src/hash/hash.c
@@ -183,6 +183,23 @@ void hash_flush(struct hash *h)
 }
 
 
+/**
+ * Clear a hashmap without dereferencing the elements
+ *
+ * @param h Hashmap table
+ */
+void hash_clear(struct hash *h)
+{
+	uint32_t i;
+
+	if (!h)
+		return;
+
+	for (i=0; i<h->bsize; i++)
+		list_clear(&h->bucket[i]);
+}
+
+
 /**
  * Calculate a valid hash size from a random size
  *
diff --git a/src/list/list.c b/src/list/list.c
index e8b4c21..5be764a 100644
--- a/src/list/list.c
+++ b/src/list/list.c
@@ -55,6 +55,31 @@ void list_flush(struct list *list)
 }
 
 
+/**
+ * Clear a linked list without dereferencing the elements
+ *
+ * @param list Linked list
+ */
+void list_clear(struct list *list)
+{
+	struct le *le;
+
+	if (!list)
+		return;
+
+	le = list->head;
+	while (le) {
+		struct le *next = le->next;
+		le->list = NULL;
+		le->prev = le->next = NULL;
+		le->data = NULL;
+		le = next;
+	}
+
+	list_init(list);
+}
+
+
 /**
  * Append a list element to a linked list
  *
diff --git a/src/sip/sip.c b/src/sip/sip.c
index 8d41948..5005b23 100644
--- a/src/sip/sip.c
+++ b/src/sip/sip.c
@@ -38,7 +38,9 @@ static void destructor(void *arg)
 	mem_deref(sip->ht_ctrans);
 
 	hash_flush(sip->ht_strans);
+	hash_clear(sip->ht_strans_mrg);
 	mem_deref(sip->ht_strans);
+	mem_deref(sip->ht_strans_mrg);
 
 	hash_flush(sip->ht_conn);
 	mem_deref(sip->ht_conn);
diff --git a/src/sip/sip.h b/src/sip/sip.h
index 1551539..94361d1 100644
--- a/src/sip/sip.h
+++ b/src/sip/sip.h
@@ -11,6 +11,7 @@ struct sip {
 	struct list reql;
 	struct hash *ht_ctrans;
 	struct hash *ht_strans;
+	struct hash *ht_strans_mrg;
 	struct hash *ht_conn;
 	struct hash *ht_udpconn;
 	struct dnsc *dnsc;
diff --git a/src/sip/strans.c b/src/sip/strans.c
index f2d4460..5d2a08f 100644
--- a/src/sip/strans.c
+++ b/src/sip/strans.c
@@ -29,6 +29,7 @@ enum state {
 
 struct sip_strans {
 	struct le he;
+	struct le he_mrg;
 	struct tmr tmr;
 	struct tmr tmrg;
 	struct sa dst;
@@ -48,6 +49,7 @@ static void destructor(void *arg)
 	struct sip_strans *st = arg;
 
 	hash_unlink(&st->he);
+	hash_unlink(&st->he_mrg);
 	tmr_cancel(&st->tmr);
 	tmr_cancel(&st->tmrg);
 	mem_deref(st->msg);
@@ -112,6 +114,30 @@ static bool cmp_cancel_handler(struct le *le, void *arg)
 }
 
 
+static bool cmp_merge_handler(struct le *le, void *arg)
+{
+	struct sip_strans *st = le->data;
+	const struct sip_msg *msg = arg;
+
+	if (pl_cmp(&st->msg->cseq.met, &msg->cseq.met))
+		return false;
+
+	if (st->msg->cseq.num != msg->cseq.num)
+		return false;
+
+	if (pl_cmp(&st->msg->callid, &msg->callid))
+		return false;
+
+	if (pl_cmp(&st->msg->from.tag, &msg->from.tag))
+		return false;
+
+	if (pl_cmp(&st->msg->ruri, &msg->ruri))
+		return false;
+
+	return true;
+}
+
+
 static void dummy_handler(void *arg)
 {
 	(void)arg;
@@ -229,6 +255,16 @@ static bool request_handler(const struct sip_msg *msg, void *arg)
 
 		return true;
 	}
+	else if (!pl_isset(&msg->to.tag)) {
+
+		st = list_ledata(hash_lookup(sip->ht_strans_mrg,
+					     hash_joaat_pl(&msg->callid),
+					     cmp_merge_handler, (void *)msg));
+		if (st) {
+			(void)sip_reply(sip, msg, 482, "Loop Detected");
+			return true;
+		}
+	}
 
 	if (!pl_strcmp(&msg->met, "CANCEL"))
 		return cancel_handler(sip, msg);
@@ -264,6 +300,9 @@ int sip_strans_alloc(struct sip_strans **stp, struct sip *sip,
 	hash_append(sip->ht_strans, hash_joaat_pl(&msg->via.branch),
 		    &st->he, st);
 
+	hash_append(sip->ht_strans_mrg, hash_joaat_pl(&msg->callid),
+		    &st->he_mrg, st);
+
 	st->invite  = !pl_strcmp(&msg->met, "INVITE");
 	st->msg     = mem_ref((void *)msg);
 	st->state   = TRYING;
@@ -367,6 +406,10 @@ int sip_strans_init(struct sip *sip, uint32_t sz)
 	if (err)
 		return err;
 
+	err = hash_alloc(&sip->ht_strans_mrg, sz);
+	if (err)
+		return err;
+
 	return hash_alloc(&sip->ht_strans, sz);
 }