diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index 243d56a938..2a290219f8 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -5575,9 +5575,14 @@ static void add_codec_to_sdp(const struct sip_pvt *p, int codec, int sample_rate
 	ast_build_string(a_buf, a_size, "a=rtpmap:%d %s/%d\r\n", rtp_code,
 			 ast_rtp_lookup_mime_subtype(1, codec),
 			 sample_rate);
-	if (codec == AST_FORMAT_G729A)
+	if (codec == AST_FORMAT_G729A) {
 		/* Indicate that we don't support VAD (G.729 annex B) */
 		ast_build_string(a_buf, a_size, "a=fmtp:%d annexb=no\r\n", rtp_code);
+	} else if (codec == AST_FORMAT_ILBC) {
+		/* Add information about us using only 20 ms packetization */
+		ast_build_string(a_buf, a_size, "a=fmtp:%d mode=20\r\n", rtp_code);
+	
+	}
 }
 
 /*! \brief Get Max T.38 Transmision rate from T38 capabilities */