--- main/rtp_engine.c	(Asterisk 11.20.0)
+++ main/rtp_engine.c	(working copy)
@@ -621,6 +622,8 @@
 			ast_format_set(&type->format, AST_FORMAT_G726_AAL2, 0);
 		}
 
+		ast_format_sdp_parse(&type->format, "");
+
 		if (instance && instance->engine && instance->engine->payload_set) {
 			instance->engine->payload_set(instance, pt, type->asterisk_format, &type->format, type->rtp_code);
 		}