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);
 
diff --git a/src/gsm_utils.c b/src/gsm_utils.c
index 4b4e2c6..31e3cd6 100644
--- a/src/gsm_utils.c
+++ b/src/gsm_utils.c
@@ -359,7 +359,11 @@
 
 enum gsm_band gsm_arfcn2band(uint16_t arfcn)
 {
-	if (arfcn & ARFCN_PCS)
+	int is_pcs = arfcn & ARFCN_PCS;
+
+	arfcn &= ~ARFCN_FLAG_MASK;
+
+	if (is_pcs)
 		return GSM_BAND_1900;
 	else if (arfcn <= 124)
 		return GSM_BAND_900;
@@ -386,8 +390,11 @@
 {
 	uint16_t freq10_ul;
 	uint16_t freq10_dl;
+	int is_pcs = arfcn & ARFCN_PCS;
 
-	if (arfcn & ARFCN_PCS) {
+	arfcn &= ~ARFCN_FLAG_MASK;
+
+	if (is_pcs) {
 		/* DCS 1900 */
 		arfcn &= ~ARFCN_PCS;
 		freq10_ul = 18502 + 2 * (arfcn-512);