diff --git a/rmw_connextdds_common/src/common/rmw_impl.cpp b/rmw_connextdds_common/src/common/rmw_impl.cpp
index bb56a933..3deb1f14 100644
--- a/rmw_connextdds_common/src/common/rmw_impl.cpp
+++ b/rmw_connextdds_common/src/common/rmw_impl.cpp
@@ -2723,7 +2723,6 @@ RMW_Connext_Client::send_request(
     reinterpret_cast<const uint32_t *>(rr_msg.gid.data)[3],
     rr_msg.sn)
 
-
   RMW_Connext_WriteParams write_params;
 
   if (DDS_RETCODE_OK !=
@@ -2737,7 +2736,9 @@ RMW_Connext_Client::send_request(
 
   rmw_ret_t rc = this->request_pub->write(&rr_msg, false /* serialized */, &write_params);
 
-  *sequence_id = write_params.sequence_number;
+  if (this->ctx->request_reply_mapping != RMW_Connext_RequestReplyMapping::Basic) {
+    *sequence_id = write_params.sequence_number;
+  }
 
   RMW_CONNEXT_LOG_DEBUG_A(
     "[%s] SENT REQUEST: "
diff --git a/rmw_connextdds_common/src/common/rmw_type_support.cpp b/rmw_connextdds_common/src/common/rmw_type_support.cpp
index c2908304..61bb65b5 100644
--- a/rmw_connextdds_common/src/common/rmw_type_support.cpp
+++ b/rmw_connextdds_common/src/common/rmw_type_support.cpp
@@ -98,10 +98,7 @@ RMW_Connext_RequestReplyMapping_Basic_serialize(
   if (RMW_RET_OK != rc) {
     return rc;
   }
-  sample_identity.sequence_number.high =
-    static_cast<DDS_Long>((rr_msg->sn & 0xFFFFFFFF00000000) >> 8);
-  sample_identity.sequence_number.low =
-    static_cast<DDS_UnsignedLong>(rr_msg->sn & 0x00000000FFFFFFFF);
+  rmw_connextdds_sn_ros_to_dds(rr_msg->sn, sample_identity.sequence_number);
 
   try {
     // Cyclone only serializes 8 bytes of the writer guid.