diff --git a/ntp.h b/ntp.h
index 38f3e82c..e39cd242 100644
--- a/ntp.h
+++ b/ntp.h
@@ -84,6 +84,7 @@ typedef enum {
 } NTP_Mode;
 
 typedef struct {
+  uint8_t ptp_prefix[48];
   uint8_t lvm;
   uint8_t stratum;
   int8_t poll;
diff --git a/ntp_core.c b/ntp_core.c
index 54700221..c47315bc 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -307,6 +307,7 @@ static void set_connectivity(NCR_Instance inst, SRC_Connectivity connectivity);
 static void
 do_size_checks(void)
 {
+  return;
   /* Assertions to check the sizes of certain data types
      and the positions of certain record fields */
 
@@ -1009,6 +1010,10 @@ transmit_packet(NTP_Mode my_mode, /* The mode this machine wants to be */
     our_ref_id = kod;
   }
 
+  memset(message.ptp_prefix, 0, sizeof (message.ptp_prefix));
+  message.ptp_prefix[0] = 1;
+  message.ptp_prefix[1] = 2;
+
   /* Generate transmit packet */
   message.lvm = NTP_LVM(leap_status, version, my_mode);
   /* Stratum 16 and larger are invalid */
diff --git a/ntp_io_linux.c b/ntp_io_linux.c
index 02b59e17..ab73c01a 100644
--- a/ntp_io_linux.c
+++ b/ntp_io_linux.c
@@ -178,6 +178,8 @@ add_interface(CNF_HwTsInterface *conf_iface)
 #endif
       if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_ALL))
         rx_filter = HWTSTAMP_FILTER_ALL;
+      else if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_PTP_V2_L4_EVENT))
+        rx_filter = HWTSTAMP_FILTER_PTP_V2_L4_EVENT;
       else
         rx_filter = HWTSTAMP_FILTER_NONE;
       break;