diff --git a/daemon/sdp.c b/daemon/sdp.c
index 41e3d89b1..cec248901 100644
--- a/daemon/sdp.c
+++ b/daemon/sdp.c
@@ -2068,28 +2068,28 @@ static void insert_codec_parameters(GString *s, struct call_media *cm,
 	}
 }
 
-void sdp_insert_media_attributes(GString *gs, union sdp_attr_print_arg a, const sdp_ng_flags *flags) {
+void sdp_insert_media_attributes(GString *gs, struct call_media *media, const sdp_ng_flags *flags) {
 	// Look up the source media. We copy the source's attributes if there is only one source
 	// media. Otherwise we skip this step.
 
-	if (a.cm->media_subscriptions.length != 1)
+	if (media->media_subscriptions.length != 1)
 		return;
 
-	__auto_type sub = a.cm->media_subscriptions.head->data;
+	__auto_type sub = media->media_subscriptions.head->data;
 	__auto_type sub_m = sub->media;
 
 	for (__auto_type l = sub_m->generic_attributes.head; l; l = l->next) {
 		__auto_type s = l->data;
-		if (s->other == ATTR_OTHER_EXTMAP && flags->strip_extmap && !MEDIA_ISSET(a.cm, PASSTHRU))
+		if (s->other == ATTR_OTHER_EXTMAP && flags->strip_extmap && !MEDIA_ISSET(media, PASSTHRU))
 			continue;
-		append_str_attr_to_gstring(gs, &s->strs.name, &s->strs.value, flags, a.cm->type_id);
+		append_str_attr_to_gstring(gs, &s->strs.name, &s->strs.value, flags, media->type_id);
 	}
 }
-void sdp_insert_monologue_attributes(GString *gs, union sdp_attr_print_arg a, const sdp_ng_flags *flags) {
+void sdp_insert_monologue_attributes(GString *gs, struct call_monologue *ml, const sdp_ng_flags *flags) {
 	// Look up the source monologue. This must be a single source monologue for all medias. If
 	// there's a mismatch or multiple source monologues, we skip this step.
 
-	struct call_monologue *source_ml = ml_medias_subscribed_to_single_ml(a.ml);
+	struct call_monologue *source_ml = ml_medias_subscribed_to_single_ml(ml);
 	if (!source_ml)
 		return;
 
diff --git a/daemon/t38.c b/daemon/t38.c
index ab53e19c9..00e168424 100644
--- a/daemon/t38.c
+++ b/daemon/t38.c
@@ -332,8 +332,8 @@ static int span_log_level_map(int level) {
 	return level;
 }
 
-void t38_insert_media_attributes(GString *gs, union sdp_attr_print_arg a, const sdp_ng_flags *flags) {
-	struct t38_gateway *tg = a.cm->t38_gateway;
+static void t38_insert_media_attributes(GString *gs, struct call_media *media, const sdp_ng_flags *flags) {
+	struct t38_gateway *tg = media->t38_gateway;
 	if (!tg)
 		return;
 
diff --git a/include/call.h b/include/call.h
index 0cc6fad52..485656e09 100644
--- a/include/call.h
+++ b/include/call.h
@@ -514,7 +514,7 @@ struct call_media {
 	struct codec_store	offered_codecs;
 	sdp_attr_q		generic_attributes;			/* sdp_attr_new() */
 	sdp_attr_q		all_attributes;			/* sdp_attr_new() */
-	sdp_attr_print_f	*sdp_attr_print;
+	sdp_media_attr_print_f	*sdp_attr_print;
 	codec_handlers_ht	codec_handlers;			/* int payload type -> struct codec_handler
 														XXX combine this with 'codecs' hash table? */
 	codec_handlers_q	codec_handlers_store;		/* storage for struct codec_handler */
@@ -633,7 +633,7 @@ struct call_monologue {
 	/* carry `sdp_session` attributes into resulting call monologue SDP */
 	sdp_attr_q		generic_attributes;
 	sdp_attr_q		all_attributes;
-	sdp_attr_print_f	*sdp_attr_print;
+	sdp_monologue_attr_print_f *sdp_attr_print;
 
 	long long moh_db_id;
 	str moh_blob;
diff --git a/include/sdp.h b/include/sdp.h
index d8811d2c6..6b4807f37 100644
--- a/include/sdp.h
+++ b/include/sdp.h
@@ -32,8 +32,8 @@ extern const str rtpe_instance_id;
 
 void sdp_init(void);
 
-sdp_attr_print_f sdp_insert_media_attributes;
-sdp_attr_print_f sdp_insert_monologue_attributes;
+void sdp_insert_media_attributes(GString *, struct call_media *, const sdp_ng_flags *);
+void sdp_insert_monologue_attributes(GString *, struct call_monologue *, const sdp_ng_flags *);
 
 void sdp_append_str_attr(GString *s, const sdp_ng_flags *flags, enum media_type media_type,
 		const str *name, const char *fmt, ...)
diff --git a/include/types.h b/include/types.h
index e98f36c34..2138fc60b 100644
--- a/include/types.h
+++ b/include/types.h
@@ -13,6 +13,9 @@ typedef struct stream_fd stream_fd;
 typedef struct rtp_payload_type rtp_payload_type;
 typedef struct sdp_origin sdp_origin;
 
+struct call_monologue;
+struct call_media;
+
 struct network_address {
 	str network_type;
 	str address_type;
@@ -31,11 +34,8 @@ struct sdp_origin {
 };
 typedef struct sdp_origin sdp_origin;
 
-union sdp_attr_print_arg {
-	struct call_media *cm;
-	struct call_monologue *ml;
-} __attribute__ ((__transparent_union__));
-typedef void sdp_attr_print_f(GString *, union sdp_attr_print_arg, const sdp_ng_flags *flags);
+typedef void sdp_monologue_attr_print_f(GString *, struct call_monologue *, const sdp_ng_flags *flags);
+typedef void sdp_media_attr_print_f(GString *, struct call_media *, const sdp_ng_flags *flags);
 
 typedef struct ng_parser ng_parser_t;
 typedef struct ng_parser_ctx ng_parser_ctx_t;