diff --git a/src/ICMP.cc b/src/ICMP.cc
index 2f11337d8a..05a6b67dff 100644
--- a/src/ICMP.cc
+++ b/src/ICMP.cc
@@ -181,6 +181,9 @@ void ICMP_Analyzer::NextICMP6(double t, const struct icmp* icmpp, int len, int c
 		case MLD_LISTENER_REDUCTION:
 #endif
 		default:
+			// Error messages (i.e., ICMPv6 type < 128) all have
+			// the same structure for their context, and are
+			// handled by the same function.
 			if ( icmpp->icmp_type < 128 )
 				Context6(t, icmpp, len, caplen, data, ip_hdr);
 			else