diff --git a/include/osmocore/gsm_utils.h b/include/osmocore/gsm_utils.h
index 7dc2388..0aadd2e 100644
--- a/include/osmocore/gsm_utils.h
+++ b/include/osmocore/gsm_utils.h
@@ -87,6 +87,7 @@
 
 #define	ARFCN_PCS	0x8000
 #define	ARFCN_UPLINK	0x4000
+#define	ARFCN_FLAG_MASK	0xf000	/* Reserve the upper 5 bits for flags */
 
 enum gsm_band gsm_arfcn2band(uint16_t arfcn);