diff --git a/ntp.h b/ntp.h
index 4e5ee92..3edc18d 100644
--- a/ntp.h
+++ b/ntp.h
@@ -47,6 +47,9 @@ typedef uint32_t NTP_int32;
 /* Maximum stratum number (infinity) */
 #define NTP_MAX_STRATUM 16
 
+/* Invalid stratum number */
+#define NTP_INVALID_STRATUM 0
+
 /* The minimum and maximum supported length of MAC */
 #define NTP_MIN_MAC_LENGTH (4 + 16)
 #define NTP_MAX_MAC_LENGTH (4 + MAX_HASH_LENGTH)
diff --git a/ntp_core.c b/ntp_core.c
index 3dde71f..0c6349f 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -241,9 +241,6 @@ static ARR_Instance broadcasts;
 /* Maximum allowed dispersion - as defined in RFC 5905 (16 seconds) */
 #define NTP_MAX_DISPERSION 16.0
 
-/* Invalid stratum number */
-#define NTP_INVALID_STRATUM 0
-
 /* Maximum allowed time for server to process client packet */
 #define MAX_SERVER_INTERVAL 4.0