diff --git a/libpri.h b/libpri.h
index 74ffe81..06b306c 100644
--- a/libpri.h
+++ b/libpri.h
@@ -142,10 +142,10 @@
 
 /* Causes for disconnection */
 #define PRI_CAUSE_UNALLOCATED					1
-#define PRI_CAUSE_NO_ROUTE_TRANSIT_NET			2
+#define PRI_CAUSE_NO_ROUTE_TRANSIT_NET			2	/* !Q.SIG */
 #define PRI_CAUSE_NO_ROUTE_DESTINATION			3
 #define PRI_CAUSE_CHANNEL_UNACCEPTABLE			6
-#define PRI_CAUSE_CALL_AWARDED_DELIVERED		7
+#define PRI_CAUSE_CALL_AWARDED_DELIVERED		7	/* !Q.SIG */
 #define PRI_CAUSE_NORMAL_CLEARING				16
 #define PRI_CAUSE_USER_BUSY						17
 #define PRI_CAUSE_NO_USER_RESPONSE				18
@@ -154,27 +154,29 @@
 #define PRI_CAUSE_NUMBER_CHANGED				22
 #define PRI_CAUSE_DESTINATION_OUT_OF_ORDER		27
 #define PRI_CAUSE_INVALID_NUMBER_FORMAT			28
-#define PRI_CAUSE_FACILITY_REJECTED				29
+#define PRI_CAUSE_FACILITY_REJECTED				29	/* !Q.SIG */
 #define PRI_CAUSE_RESPONSE_TO_STATUS_ENQUIRY	30
 #define PRI_CAUSE_NORMAL_UNSPECIFIED			31
 #define PRI_CAUSE_NORMAL_CIRCUIT_CONGESTION		34
-#define PRI_CAUSE_NETWORK_OUT_OF_ORDER			38
+#define PRI_CAUSE_NETWORK_OUT_OF_ORDER			38	/* !Q.SIG */
 #define PRI_CAUSE_NORMAL_TEMPORARY_FAILURE		41
-#define PRI_CAUSE_SWITCH_CONGESTION				42
-#define PRI_CAUSE_ACCESS_INFO_DISCARDED			43
+#define PRI_CAUSE_SWITCH_CONGESTION				42	/* !Q.SIG */
+#define PRI_CAUSE_ACCESS_INFO_DISCARDED			43	/* !Q.SIG */
 #define PRI_CAUSE_REQUESTED_CHAN_UNAVAIL		44
-#define PRI_CAUSE_PRE_EMPTED					45
-#define PRI_CAUSE_FACILITY_NOT_SUBSCRIBED  		50
-#define PRI_CAUSE_OUTGOING_CALL_BARRED     		52
-#define PRI_CAUSE_INCOMING_CALL_BARRED     		54
+#define PRI_CAUSE_PRE_EMPTED					45	/* !Q.SIG */
+#define PRI_CAUSE_FACILITY_NOT_SUBSCRIBED  		50	/* !Q.SIG */
+#define PRI_CAUSE_OUTGOING_CALL_BARRED     		52	/* !Q.SIG */
+#define PRI_CAUSE_INCOMING_CALL_BARRED     		54	/* !Q.SIG */
 #define PRI_CAUSE_BEARERCAPABILITY_NOTAUTH		57
 #define PRI_CAUSE_BEARERCAPABILITY_NOTAVAIL     58
+#define PRI_CAUSE_SERVICEOROPTION_NOTAVAIL		63	/* Q.SIG */
 #define PRI_CAUSE_BEARERCAPABILITY_NOTIMPL		65
-#define PRI_CAUSE_CHAN_NOT_IMPLEMENTED     		66
-#define PRI_CAUSE_FACILITY_NOT_IMPLEMENTED      69
+#define PRI_CAUSE_CHAN_NOT_IMPLEMENTED     		66	/* !Q.SIG */
+#define PRI_CAUSE_FACILITY_NOT_IMPLEMENTED      69	/* !Q.SIG */
 #define PRI_CAUSE_INVALID_CALL_REFERENCE		81
+#define PRI_CAUSE_IDENTIFIED_CHANNEL_NOTEXIST	82	/* Q.SIG */
 #define PRI_CAUSE_INCOMPATIBLE_DESTINATION		88
-#define PRI_CAUSE_INVALID_MSG_UNSPECIFIED  		95
+#define PRI_CAUSE_INVALID_MSG_UNSPECIFIED  		95	/* !Q.SIG */
 #define PRI_CAUSE_MANDATORY_IE_MISSING			96
 #define PRI_CAUSE_MESSAGE_TYPE_NONEXIST			97
 #define PRI_CAUSE_WRONG_MESSAGE					98
@@ -182,9 +184,9 @@
 #define PRI_CAUSE_INVALID_IE_CONTENTS			100
 #define PRI_CAUSE_WRONG_CALL_STATE				101
 #define PRI_CAUSE_RECOVERY_ON_TIMER_EXPIRE		102
-#define PRI_CAUSE_MANDATORY_IE_LENGTH_ERROR		103
+#define PRI_CAUSE_MANDATORY_IE_LENGTH_ERROR		103	/* !Q.SIG */
 #define PRI_CAUSE_PROTOCOL_ERROR				111
-#define PRI_CAUSE_INTERWORKING					127
+#define PRI_CAUSE_INTERWORKING					127	/* !Q.SIG */
 
 /* Transmit capabilities */
 #define PRI_TRANS_CAP_SPEECH					0x0
diff --git a/q931.c b/q931.c
index b254f1b..3f1186a 100644
--- a/q931.c
+++ b/q931.c
@@ -120,9 +120,11 @@ struct msgtype causes[] = {
 	{ PRI_CAUSE_BEARERCAPABILITY_NOTAUTH, "Bearer capability not authorized" },
 	{ PRI_CAUSE_BEARERCAPABILITY_NOTAVAIL, "Bearer capability not available" },
 	{ PRI_CAUSE_BEARERCAPABILITY_NOTIMPL, "Bearer capability not implemented" },
+	{ PRI_CAUSE_SERVICEOROPTION_NOTAVAIL, "Service or option not available, unspecified" },
 	{ PRI_CAUSE_CHAN_NOT_IMPLEMENTED, "Channel not implemented" },
 	{ PRI_CAUSE_FACILITY_NOT_IMPLEMENTED, "Facility not implemented" },
 	{ PRI_CAUSE_INVALID_CALL_REFERENCE, "Invalid call reference value" },
+	{ PRI_CAUSE_IDENTIFIED_CHANNEL_NOTEXIST, "Identified channel does not exist" },
 	{ PRI_CAUSE_INCOMPATIBLE_DESTINATION, "Incompatible destination" },
 	{ PRI_CAUSE_INVALID_MSG_UNSPECIFIED, "Invalid message unspecified" },
 	{ PRI_CAUSE_MANDATORY_IE_MISSING, "Mandatory information element is missing" },
@@ -1531,11 +1533,11 @@ static char *pri_causeclass2str(int cause)
 	static struct msgtype causeclasses[] = {
 		{ 0, "Normal Event" },
 		{ 1, "Normal Event" },
-		{ 2, "Network Congestion" },
+		{ 2, "Network Congestion (resource unavailable)" },
 		{ 3, "Service or Option not Available" },
 		{ 4, "Service or Option not Implemented" },
-		{ 5, "Invalid message" },
-		{ 6, "Protocol Error" },
+		{ 5, "Invalid message (e.g. parameter out of range)" },
+		{ 6, "Protocol Error (e.g. unknown message)" },
 		{ 7, "Interworking" },
 	};
 	return code2str(cause, causeclasses, sizeof(causeclasses) / sizeof(causeclasses[0]));