diff --git a/README.md b/README.md
index 9c5b37cd9..f6a4e9762 100644
--- a/README.md
+++ b/README.md
@@ -1100,6 +1100,10 @@ Optionally included keys are:
 		Additional options that can be appended to the codec string with additional slashes
 		are ptime and the `fmtp` string, for example `iLBC/8000/1///mode=30`.
 
+		If a literal `=` cannot be used due to parsing constraints (i.e. being wrongly
+		interpreted as a key-value pair), it can be escaped by using two dashes instead,
+		e.g. `iLBC/8000/1///mode--30`.
+
 		As a special case, if the `strip=all` option has been used and the `transcode`
 		option is used on a codec that was originally present in the offer, then
 		*rtpengine* will treat this codec the same as if it had been used with the `offer`
diff --git a/daemon/call_interfaces.c b/daemon/call_interfaces.c
index 242b4ee0b..bd45429b7 100644
--- a/daemon/call_interfaces.c
+++ b/daemon/call_interfaces.c
@@ -704,25 +704,35 @@ static void call_ng_flags_supports(struct sdp_ng_flags *out, str *s, void *dummy
 	if (!str_cmp(s, "load limit"))
 		out->supports_load_limit = 1;
 }
+static str *str_dup_escape(const str *s) {
+	str *ret = str_dup(s);
+	int i;
+	while ((i = str_str(ret, "--")) >= 0) {
+		ret->s[i] = '=';
+		memmove(&ret->s[i + 1], &ret->s[i + 2], ret->len - i - 2);
+		ret->len--;
+	}
+	return ret;
+}
 static void call_ng_flags_codec_list(struct sdp_ng_flags *out, str *s, void *qp) {
-	str *s_copy = str_slice_dup(s);
+	str *s_copy = str_dup_escape(s);
 	g_queue_push_tail((GQueue *) qp, s_copy);
 }
 static void call_ng_flags_str_ht(struct sdp_ng_flags *out, str *s, void *htp) {
-	str *s_copy = str_slice_dup(s);
+	str *s_copy = str_dup_escape(s);
 	GHashTable **ht = htp;
 	if (!*ht)
-		*ht = g_hash_table_new_full(str_case_hash, str_case_equal, str_slice_free, NULL);
+		*ht = g_hash_table_new_full(str_case_hash, str_case_equal, free, NULL);
 	g_hash_table_replace(*ht, s_copy, s_copy);
 }
 #ifdef WITH_TRANSCODING
 static void call_ng_flags_str_ht_split(struct sdp_ng_flags *out, str *s, void *htp) {
 	GHashTable **ht = htp;
 	if (!*ht)
-		*ht = g_hash_table_new_full(str_case_hash, str_case_equal, str_slice_free, str_slice_free);
+		*ht = g_hash_table_new_full(str_case_hash, str_case_equal, free, free);
 	str splitter = *s;
 	while (1) {
-		g_hash_table_replace(*ht, str_slice_dup(&splitter), str_slice_dup(s));
+		g_hash_table_replace(*ht, str_dup_escape(&splitter), str_dup_escape(s));
 		char *c = memrchr(splitter.s, '/', splitter.len);
 		if (!c)
 			break;
@@ -1009,8 +1019,8 @@ static void call_ng_free_flags(struct sdp_ng_flags *flags) {
 		g_hash_table_destroy(flags->codec_set);
 	if (flags->sdes_no)
 		g_hash_table_destroy(flags->sdes_no);
-	g_queue_clear_full(&flags->codec_offer, str_slice_free);
-	g_queue_clear_full(&flags->codec_transcode, str_slice_free);
+	g_queue_clear_full(&flags->codec_offer, free);
+	g_queue_clear_full(&flags->codec_transcode, free);
 }
 
 static enum load_limit_reasons call_offer_session_limit(void) {
diff --git a/daemon/codec.c b/daemon/codec.c
index fef965222..db1eff722 100644
--- a/daemon/codec.c
+++ b/daemon/codec.c
@@ -2129,7 +2129,6 @@ static int __codec_synth_transcode_options(struct rtp_payload_type *pt, struct s
 	if (pt->clock_rate != 1)
 		return 0;
 
-	struct call *call = media->call;
 	GHashTable *clockrates = g_hash_table_new(g_direct_hash, g_direct_equal);
 
 	// special handling - add one instance for each clock rate that is present
@@ -2137,17 +2136,13 @@ static int __codec_synth_transcode_options(struct rtp_payload_type *pt, struct s
 		struct rtp_payload_type *pt_r = k->data;
 		if (g_hash_table_lookup(clockrates, GUINT_TO_POINTER(pt_r->clock_rate)))
 			continue;
-		char *pt_s;
-		if (asprintf(&pt_s, STR_FORMAT "/%u", STR_FMT(&pt->encoding), pt_r->clock_rate) < 0)
-			continue;
-		pt_s = call_strdup(call, pt_s);
-		// XXX optimise this -^  call buffer can probably be replaced with a gstringchunk
-		// and made lock free
+		char *pt_s = g_strdup_printf(STR_FORMAT "/%u", STR_FMT(&pt->encoding), pt_r->clock_rate);
 		g_hash_table_insert(clockrates, GUINT_TO_POINTER(pt_r->clock_rate), (void *) 1);
 		str pt_str;
 		str_init(&pt_str, pt_s);
 		ilog(LOG_DEBUG, "Synthesised transcoding option for '%s'", pt_s);
-		g_queue_push_tail(&flags->codec_transcode, str_slice_dup(&pt_str));
+		g_queue_push_tail(&flags->codec_transcode, str_dup(&pt_str));
+		g_free(pt_s);
 	}
 
 	payload_type_free(pt);