diff --git a/library/RLCMAC_Types.ttcn b/library/RLCMAC_Types.ttcn
index 6231a54..52aaef8 100644
--- a/library/RLCMAC_Types.ttcn
+++ b/library/RLCMAC_Types.ttcn
@@ -204,10 +204,11 @@
 			     ctrl, mac_hdr.payload_type = MAC_PT_RLCMAC_OPT)"
 	};
 
-	external function enc_RlcmacUlBlock(in RlcmacUlBlock si) return octetstring
-		with { extension "prototype(convert) encode(RAW)" };
-	external function dec_RlcmacUlBlock(in octetstring stream) return RlcmacUlBlock
-		with { extension "prototype(convert) decode(RAW)" };
+	/* as the sub-types (RlcmacDl*Block) are not using the RAW coder, we cannot
+	 * use auto-generated functions here, as they would decode those sub-types
+	 * based on the RAW coder, not baed on the manual C++ functions */
+	external function enc_RlcmacUlBlock(in RlcmacUlBlock si) return octetstring;
+	external function dec_RlcmacUlBlock(in octetstring stream) return RlcmacUlBlock;
 
 	type union RlcmacDlBlock {
 		RlcmacDlDataBlock	data,
@@ -218,9 +219,10 @@
 			     ctrl, mac_hdr.payload_type = MAC_PT_RLCMAC_OPT)"
 	};
 
-	external function enc_RlcmacDlBlock(in RlcmacDlBlock si) return octetstring
-		with { extension "prototype(convert) encode(RAW)" };
-	external function dec_RlcmacDlBlock(in octetstring stream) return RlcmacDlBlock
-		with { extension "prototype(convert) decode(RAW)" };
+	/* as the sub-types (RlcmacDl*Block) are not using the RAW coder, we cannot
+	 * use auto-generated functions here, as they would decode those sub-types
+	 * based on the RAW coder, not baed on the manual C++ functions */
+	external function enc_RlcmacDlBlock(in RlcmacDlBlock si) return octetstring;
+	external function dec_RlcmacDlBlock(in octetstring stream) return RlcmacDlBlock;
 
 } with { encode "RAW"; variant "FIELDORDER(msb)" }