diff --git a/nest/a-path.c b/nest/a-path.c
index b6a30f54..cffd46ab 100644
--- a/nest/a-path.c
+++ b/nest/a-path.c
@@ -25,7 +25,7 @@
 #define BAD(DSC, VAL) ({ err_dsc = DSC; err_val = VAL; goto bad; })
 
 int
-as_path_valid(byte *data, uint len, int bs, int confed, char *err, uint elen)
+as_path_valid(byte *data, uint len, int bs, int sets, int confed, char *err, uint elen)
 {
   byte *pos = data;
   char *err_dsc = NULL;
@@ -46,13 +46,21 @@ as_path_valid(byte *data, uint len, int bs, int confed, char *err, uint elen)
     switch (type)
     {
     case AS_PATH_SET:
+      if (!sets)
+	BAD("AS_SET segment", type);
+      break;
+
     case AS_PATH_SEQUENCE:
       break;
 
     case AS_PATH_CONFED_SEQUENCE:
-    case AS_PATH_CONFED_SET:
       if (!confed)
-	BAD("AS_CONFED* segment", type);
+	BAD("AS_CONFED_SEQUENCE segment", type);
+      break;
+
+    case AS_PATH_CONFED_SET:
+      if (!sets || !confed)
+	BAD("AS_CONFED_SET segment", type);
       break;
 
     default:
diff --git a/nest/attrs.h b/nest/attrs.h
index 6fb0a8fa..3a4b0acd 100644
--- a/nest/attrs.h
+++ b/nest/attrs.h
@@ -30,7 +30,7 @@
 
 struct f_tree;
 
-int as_path_valid(byte *data, uint len, int bs, int confed, char *err, uint elen);
+int as_path_valid(byte *data, uint len, int bs, int sets, int confed, char *err, uint elen);
 int as_path_16to32(byte *dst, const byte *src, uint len);
 int as_path_32to16(byte *dst, const byte *src, uint len);
 int as_path_contains_as4(const struct adata *path);
diff --git a/proto/bgp/attrs.c b/proto/bgp/attrs.c
index 9a4e12d2..9b243763 100644
--- a/proto/bgp/attrs.c
+++ b/proto/bgp/attrs.c
@@ -426,10 +426,11 @@ bgp_decode_as_path(struct bgp_parse_state *s, uint code UNUSED, uint flags, byte
 {
   struct bgp_proto *p = s->proto;
   int as_length = s->as4_session ? 4 : 2;
+  int as_sets = p->cf->allow_as_sets;
   int as_confed = p->cf->confederation && p->is_interior;
   char err[128];
 
-  if (!as_path_valid(data, len, as_length, as_confed, err, sizeof(err)))
+  if (!as_path_valid(data, len, as_length, as_sets, as_confed, err, sizeof(err)))
     WITHDRAW("Malformed AS_PATH attribute - %s", err);
 
   /* In some circumstances check for initial AS_CONFED_SEQUENCE; RFC 5065 5.0 */
@@ -763,6 +764,9 @@ bgp_decode_as4_aggregator(struct bgp_parse_state *s, uint code UNUSED, uint flag
 static void
 bgp_decode_as4_path(struct bgp_parse_state *s, uint code UNUSED, uint flags, byte *data, uint len, ea_list **to)
 {
+  struct bgp_proto *p = s->proto;
+  int sets = p->cf->allow_as_sets;
+
   char err[128];
 
   if (s->as4_session)
@@ -771,7 +775,7 @@ bgp_decode_as4_path(struct bgp_parse_state *s, uint code UNUSED, uint flags, byt
   if (len < 6)
     DISCARD(BAD_LENGTH, "AS4_PATH", len);
 
-  if (!as_path_valid(data, len, 4, 1, err, sizeof(err)))
+  if (!as_path_valid(data, len, 4, sets, 1, err, sizeof(err)))
     DISCARD("Malformed AS4_PATH attribute - %s", err);
 
   struct adata *a = lp_alloc_adata(s->pool, len);
diff --git a/proto/bgp/bgp.h b/proto/bgp/bgp.h
index d3e8f2ff..1270b8f3 100644
--- a/proto/bgp/bgp.h
+++ b/proto/bgp/bgp.h
@@ -107,6 +107,7 @@ struct bgp_config {
   int interpret_communities;		/* Hardwired handling of well-known communities */
   int allow_local_as;			/* Allow that number of local ASNs in incoming AS_PATHs */
   int allow_local_pref;			/* Allow LOCAL_PREF in EBGP sessions */
+  int allow_as_sets;			/* Allow AS_SETs in incoming AS_PATHs */
   int gr_mode;				/* Graceful restart mode (BGP_GR_*) */
   int llgr_mode;			/* Long-lived graceful restart mode (BGP_LLGR_*) */
   int setkey;				/* Set MD5 password to system SA/SP database */
diff --git a/proto/bgp/config.Y b/proto/bgp/config.Y
index 692854cf..090ba24e 100644
--- a/proto/bgp/config.Y
+++ b/proto/bgp/config.Y
@@ -29,7 +29,7 @@ CF_KEYWORDS(BGP, LOCAL, NEIGHBOR, AS, HOLD, TIME, CONNECT, RETRY, KEEPALIVE,
 	SECURITY, DETERMINISTIC, SECONDARY, ALLOW, BFD, ADD, PATHS, RX, TX,
 	GRACEFUL, RESTART, AWARE, CHECK, LINK, PORT, EXTENDED, MESSAGES, SETKEY,
 	STRICT, BIND, CONFEDERATION, MEMBER, MULTICAST, FLOW4, FLOW6, LONG,
-	LIVED, STALE, IMPORT, IBGP, EBGP, MANDATORY, INTERNAL, EXTERNAL,
+	LIVED, STALE, IMPORT, IBGP, EBGP, MANDATORY, INTERNAL, EXTERNAL, SETS,
 	DYNAMIC, RANGE, NAME, DIGITS, BGP_AIGP, AIGP, ORIGINATE, COST)
 
 %type <i> bgp_nh
@@ -63,6 +63,7 @@ bgp_proto_start: proto_start BGP {
      BGP_CFG->enable_as4 = 1;
      BGP_CFG->capabilities = 2;
      BGP_CFG->interpret_communities = 1;
+     BGP_CFG->allow_as_sets = 1;
      BGP_CFG->default_local_pref = 100;
      BGP_CFG->gr_mode = BGP_GR_AWARE;
      BGP_CFG->gr_time = 120;
@@ -179,6 +180,7 @@ bgp_proto:
  | bgp_proto ALLOW LOCAL AS ';' { BGP_CFG->allow_local_as = -1; }
  | bgp_proto ALLOW LOCAL AS expr ';' { BGP_CFG->allow_local_as = $5; }
  | bgp_proto ALLOW BGP_LOCAL_PREF bool ';' { BGP_CFG->allow_local_pref = $4; }
+ | bgp_proto ALLOW AS SETS bool ';' { BGP_CFG->allow_as_sets = $5; }
  | bgp_proto GRACEFUL RESTART bool ';' { BGP_CFG->gr_mode = $4; }
  | bgp_proto GRACEFUL RESTART AWARE ';' { BGP_CFG->gr_mode = BGP_GR_AWARE; }
  | bgp_proto GRACEFUL RESTART TIME expr ';' { BGP_CFG->gr_time = $5; }