diff --git a/ntp.h b/ntp.h
index 5ea5ef6..52b2ab5 100644
--- a/ntp.h
+++ b/ntp.h
@@ -113,6 +113,23 @@ typedef struct {
 #define NTP_REFID_LOCAL 0x7F7F0101UL /* 127.127.1.1 */
 #define NTP_REFID_SMOOTH 0x7F7F01FFUL /* 127.127.1.255 */
 
+/* Non-authentication extension fields and corresponding internal flags */
+
+#define NTP_EF_EXP1                     0xF323
+
+#define NTP_EF_FLAG_EXP1                0x1
+
+/* Pre-NTPv5 experimental extension field */
+typedef struct {
+  uint32_t magic;
+  NTP_int32 root_delay;
+  NTP_int32 root_dispersion;
+  NTP_int64 mono_receive_ts;
+  uint32_t mono_epoch;
+} NTP_ExtFieldExp1;
+
+#define NTP_EF_EXP1_MAGIC 0xF5BEDD9AU
+
 /* Authentication extension fields */
 
 #define NTP_EF_NTS_UNIQUE_IDENTIFIER    0x0104
diff --git a/ntp_core.c b/ntp_core.c
index 5455964..9eb6758 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -1406,6 +1406,11 @@ parse_packet(NTP_Packet *packet, int length, NTP_PacketInfo *info)
       case NTP_EF_NTS_AUTH_AND_EEF:
         info->auth.mode = NTP_AUTH_NTS;
         break;
+      case NTP_EF_EXP1:
+        if (ef_body_length == sizeof (NTP_ExtFieldExp1) &&
+            ntohl(((NTP_ExtFieldExp1 *)ef_body)->magic) == NTP_EF_EXP1_MAGIC)
+          info->ext_field_flags |= NTP_EF_FLAG_EXP1;
+        break;
       default:
         DEBUG_LOG("Unknown extension field type=%x", (unsigned int)ef_type);
     }