diff --git a/33128/r18/TS33128Payloads.asn b/33128/r18/TS33128Payloads.asn
index 95a474f32b01f627ae891968b6cea316d76f6da5..7904e0943a4829cfafb66f7e4b213b1ce1660266 100644
--- a/33128/r18/TS33128Payloads.asn
+++ b/33128/r18/TS33128Payloads.asn
@@ -425,8 +425,14 @@ CCPDU ::= CHOICE
     uPFCCPDU            [1] UPFCCPDU,
     extendedUPFCCPDU    [2] ExtendedUPFCCPDU,
     mMSCCPDU            [3] MMSCCPDU,
+
+    -- In Rel-16 (threeGPP(4) ts33128(19) r16(16) version9(9)),
+    -- tag 4 is pTCCCPDU and tag 5 is not used.
+    -- Rel-17 or newer decoders should decode tag 4 contents as PTCCCPDU if
+    -- r16 is used in cCPayloadOID.
     nIDDCCPDU           [4] NIDDCCPDU,
     pTCCCPDU            [5] PTCCCPDU,
+
     iMSCCPDU            [6] IMSCCPDU
 }