diff --git a/include/osmocom/gsm/mncc.h b/include/osmocom/gsm/mncc.h
index 7e7d12c..e5e9607 100644
--- a/include/osmocom/gsm/mncc.h
+++ b/include/osmocom/gsm/mncc.h
@@ -15,7 +15,7 @@
 	int		coding;		/* Coding Standard */
 	int		radio;		/* Radio Channel Requirement */
 	int		speech_ctm;	/* CTM text telephony indication */
-	int		speech_ver[8];	/* Speech version indication */
+	int		speech_ver[8];	/* Speech version indication, see enum gsm48_bcap_speech_ver; -1 marks end */
 	struct {
 		enum gsm48_bcap_ra		rate_adaption;
 		enum gsm48_bcap_sig_access	sig_access;