diff --git a/33128/r16/TS33128Payloads.asn b/33128/r16/TS33128Payloads.asn
index 6576c098961d79b55661c2e2f7236a7aea5b0869..05bdfbd269949531a2a9f7fe0024b7089a76c6a9 100644
--- a/33128/r16/TS33128Payloads.asn
+++ b/33128/r16/TS33128Payloads.asn
@@ -254,7 +254,15 @@ CCPDU ::= CHOICE
     uPFCCPDU            [1] UPFCCPDU,
     extendedUPFCCPDU    [2] ExtendedUPFCCPDU,
     mMSCCPDU            [3] MMSCCPDU,
+
+    -- In Rel-17 and newer (threeGPP(4) ts33128(19) r17(17) version1(1)),
+    -- tag 4 is nIDDCCPDU and tag 5 is pTCCCPDU.
+    -- Rel-16 decoders should not decode tag 4 contents as PTCCCPDU if
+    -- r17 or newer is used in cCPayloadOID.
     pTCCCPDU            [4] PTCCCPDU
+
+    -- Tag 5 is reserved for pTCCCPDU in Rel-17 and newer.
+
 }
 
 -- ===========================