diff --git a/33128/r17/TS33128Payloads.asn b/33128/r17/TS33128Payloads.asn
index 1304ee377f4ad5586c008855debf20ff46c6a267..212e8720f5747c288d6a7c0b0c73df36cb5db083 100644
--- a/33128/r17/TS33128Payloads.asn
+++ b/33128/r17/TS33128Payloads.asn
@@ -397,8 +397,14 @@ 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
 }