Index: main/format_cap.c
===================================================================
--- main/format_cap.c	(revision 385594)
+++ main/format_cap.c	(working copy)
@@ -161,6 +161,9 @@
 
 void ast_format_cap_append(struct ast_format_cap *dst, const struct ast_format_cap *src)
 {
+	if (!src || !src->formats) {
+		return;
+	}
 	ao2_callback(src->formats, OBJ_NODATA, append_cb, dst);
 }
 
Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 385594)
+++ channels/chan_sip.c	(working copy)
@@ -32646,7 +32657,12 @@
 static void sip_get_codec(struct ast_channel *chan, struct ast_format_cap *result)
 {
 	struct sip_pvt *p = ast_channel_tech_pvt(chan);
-	ast_format_cap_append(result, ast_format_cap_is_empty(p->peercaps) ? p->caps : p->peercaps);
+
+	if (!ast_format_cap_is_empty(p->peercaps)) {
+		ast_format_cap_append(result, p->peercaps);
+	} else if (!ast_format_cap_is_empty(p->caps)) {
+		ast_format_cap_append(result, p->caps);
+	} 
 }
 
 static struct ast_rtp_glue sip_rtp_glue = {