diff --git a/lib/codeclib.c b/lib/codeclib.c
index f37f0dc40..0bb81b61f 100644
--- a/lib/codeclib.c
+++ b/lib/codeclib.c
@@ -1625,8 +1625,13 @@ void codeclib_init(int print) {
 		const struct rtp_payload_type *pt = rtp_get_rfc_codec(&def->rtpname_str);
 		if (pt)
 			def->rfc_payload_type = pt->payload_type;
-		else
-			def->rfc_payload_type = -1;
+		else {
+			// special case:
+			if (!strcmp(def->rtpname, "G729a"))
+				def->rfc_payload_type = 18;
+			else
+				def->rfc_payload_type = -1;
+		}
 
 		if (def->codec_type && def->codec_type->def_init)
 			def->codec_type->def_init(def);
diff --git a/lib/rtplib.c b/lib/rtplib.c
index 766404c9e..9f6359e4e 100644
--- a/lib/rtplib.c
+++ b/lib/rtplib.c
@@ -150,8 +150,25 @@ bool rtp_payload_type_fmt_eq_nf(const struct rtp_payload_type *a, const struct r
 		return false;
 	if (a->channels != b->channels)
 		return false;
-	if (str_casecmp_str(&a->encoding, &b->encoding))
+	if (str_casecmp_str(&a->encoding, &b->encoding)) {
+#ifdef WITH_TRANSCODING
+		// last ditch effort: see if it's a botched alias name (AKA G729a)
+		if (!a->codec_def || !b->codec_def)
+			return false;
+		if (a->codec_def->rfc_payload_type == -1 || b->codec_def->rfc_payload_type == -1)
+			return false;
+		if (a->codec_def->rfc_payload_type != b->codec_def->rfc_payload_type)
+			return false;
+		if (a->codec_def->codec_type != b->codec_def->codec_type)
+			return false;
+		if (a->codec_def->avcodec_id != b->codec_def->avcodec_id)
+			return false;
+		// consider them the same
+		return true;
+#else
 		return false;
+#endif
+	}
 	return true;
 }
 
@@ -160,9 +177,10 @@ bool rtp_payload_type_fmt_eq_nf(const struct rtp_payload_type *a, const struct r
 int rtp_payload_type_fmt_cmp(const struct rtp_payload_type *a, const struct rtp_payload_type *b) {
 	if (!rtp_payload_type_fmt_eq_nf(a, b))
 		return -1;
-	if (a->codec_def && a->codec_def == b->codec_def) {
-		if (a->codec_def->format_cmp)
-			return a->codec_def->format_cmp(a, b);
+	if (a->codec_def && b->codec_def
+			&& a->codec_def->format_cmp
+			&& a->codec_def->format_cmp == b->codec_def->format_cmp) {
+		return a->codec_def->format_cmp(a, b);
 	}
 	if (!a->codec_def) // ignore format of codecs we don't know
 		return 0;
diff --git a/t/auto-daemon-tests.pl b/t/auto-daemon-tests.pl
index 79f79e63a..46ae86ea5 100755
--- a/t/auto-daemon-tests.pl
+++ b/t/auto-daemon-tests.pl
@@ -294,6 +294,8 @@ a=sendrecv
 a=rtcp:PORT
 SDP
 
+if ($extended_tests) {
+
 new_call;
 
 offer('mismatched G.729 annexb', { }, <<SDP);
@@ -418,6 +420,195 @@ a=rtcp:PORT
 a=ptime:20
 SDP
 
+
+new_call;
+
+offer('rtpmap default mismatched G.729 annexb', { }, <<SDP);
+v=0
+o=- 13111259 1 IN IP4 1.2.3.4
+s=-
+c=IN IP4 1.2.3.4
+t=0 0
+m=audio 23874 RTP/AVP 9 8 0 18 100
+a=rtpmap:100 telephone-event/8000
+a=ptime:20
+----------------------------
+v=0
+o=- 13111259 1 IN IP4 1.2.3.4
+s=-
+c=IN IP4 203.0.113.1
+t=0 0
+m=audio PORT RTP/AVP 9 8 0 18 100
+a=rtpmap:9 G722/8000
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:18 G729/8000
+a=rtpmap:100 telephone-event/8000
+a=sendrecv
+a=rtcp:PORT
+a=ptime:20
+SDP
+
+answer('rtpmap default mismatched G.729 annexb', { }, <<SDP);
+v=0
+o=- 1737116508926565 1737116508926565 IN IP4 5.6.7.7
+s=SIP call
+c=IN IP4 5.6.7.7
+t=0 0
+m=audio 49696 RTP/AVP 8 0 18 100
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:18 G729a/8000
+a=rtpmap:100 telephone-event/8000
+a=fmtp:100 0-11
+a=ptime:20
+a=maxptime:30
+a=sendrecv
+----------------------------
+v=0
+o=- 1737116508926565 1737116508926565 IN IP4 5.6.7.7
+s=SIP call
+c=IN IP4 203.0.113.1
+t=0 0
+m=audio PORT RTP/AVP 8 0 18 100
+a=maxptime:30
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:18 G729a/8000
+a=rtpmap:100 telephone-event/8000
+a=fmtp:100 0-11
+a=sendrecv
+a=rtcp:PORT
+a=ptime:20
+SDP
+
+new_call;
+
+offer('rtpmap mismatched G.729 annexb', { }, <<SDP);
+v=0
+o=- 13111259 1 IN IP4 1.2.3.4
+s=-
+c=IN IP4 1.2.3.4
+t=0 0
+m=audio 23874 RTP/AVP 9 8 0 18 100
+a=rtpmap:100 telephone-event/8000
+a=ptime:20
+----------------------------
+v=0
+o=- 13111259 1 IN IP4 1.2.3.4
+s=-
+c=IN IP4 203.0.113.1
+t=0 0
+m=audio PORT RTP/AVP 9 8 0 18 100
+a=rtpmap:9 G722/8000
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:18 G729/8000
+a=rtpmap:100 telephone-event/8000
+a=sendrecv
+a=rtcp:PORT
+a=ptime:20
+SDP
+
+answer('rtpmap mismatched G.729 annexb', { }, <<SDP);
+v=0
+o=- 1737116508926565 1737116508926565 IN IP4 5.6.7.7
+s=SIP call
+c=IN IP4 5.6.7.7
+t=0 0
+m=audio 49696 RTP/AVP 8 0 18 100
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:18 G729a/8000
+a=fmtp:18 annexb=no
+a=rtpmap:100 telephone-event/8000
+a=fmtp:100 0-11
+a=ptime:20
+a=maxptime:30
+a=sendrecv
+----------------------------
+v=0
+o=- 1737116508926565 1737116508926565 IN IP4 5.6.7.7
+s=SIP call
+c=IN IP4 203.0.113.1
+t=0 0
+m=audio PORT RTP/AVP 8 0 18 100
+a=maxptime:30
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:18 G729a/8000
+a=fmtp:18 annexb=no
+a=rtpmap:100 telephone-event/8000
+a=fmtp:100 0-11
+a=sendrecv
+a=rtcp:PORT
+a=ptime:20
+SDP
+
+new_call;
+
+offer('actually rtpmap mismatched G.729 annexb', { }, <<SDP);
+v=0
+o=- 13111259 1 IN IP4 1.2.3.4
+s=-
+c=IN IP4 1.2.3.4
+t=0 0
+m=audio 23874 RTP/AVP 9 8 0 18 100
+a=rtpmap:100 telephone-event/8000
+a=ptime:20
+----------------------------
+v=0
+o=- 13111259 1 IN IP4 1.2.3.4
+s=-
+c=IN IP4 203.0.113.1
+t=0 0
+m=audio PORT RTP/AVP 9 8 0 18 100
+a=rtpmap:9 G722/8000
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:18 G729/8000
+a=rtpmap:100 telephone-event/8000
+a=sendrecv
+a=rtcp:PORT
+a=ptime:20
+SDP
+
+answer('actually rtpmap mismatched G.729 annexb', { }, <<SDP);
+v=0
+o=- 1737116508926565 1737116508926565 IN IP4 5.6.7.7
+s=SIP call
+c=IN IP4 5.6.7.7
+t=0 0
+m=audio 49696 RTP/AVP 8 0 18 100
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:18 G729a/8000
+a=fmtp:18 annexb=yes
+a=rtpmap:100 telephone-event/8000
+a=fmtp:100 0-11
+a=ptime:20
+a=maxptime:30
+a=sendrecv
+----------------------------
+v=0
+o=- 1737116508926565 1737116508926565 IN IP4 5.6.7.7
+s=SIP call
+c=IN IP4 203.0.113.1
+t=0 0
+m=audio PORT RTP/AVP 8 0 100
+a=maxptime:30
+a=rtpmap:8 PCMA/8000
+a=rtpmap:0 PCMU/8000
+a=rtpmap:100 telephone-event/8000
+a=fmtp:100 0-11
+a=sendrecv
+a=rtcp:PORT
+a=ptime:20
+SDP
+
+}
+
+
 new_call;
 
 offer('original sendrecv control', { }, <<SDP);