diff --git a/include/osmocom/gsm/protocol/gsm_04_08.h b/include/osmocom/gsm/protocol/gsm_04_08.h
index 074c258..e442c7f 100644
--- a/include/osmocom/gsm/protocol/gsm_04_08.h
+++ b/include/osmocom/gsm/protocol/gsm_04_08.h
@@ -6,7 +6,6 @@
 #include <osmocom/core/utils.h>
 #include <osmocom/core/endian.h>
 
-
 /* GSM TS 04.08  definitions */
 struct gsm_lchan;
 
@@ -925,6 +924,8 @@
 #define GSM48_PDISC_MASK	0x0f
 #define GSM48_PDISC_USSD	0x11
 
+bool gsm48_hdr_gmm_cipherable(const struct gsm48_hdr *hdr);
+
 static inline uint8_t gsm48_hdr_pdisc(const struct gsm48_hdr *hdr)
 {
 	/*