diff --git a/include/osmocom/gsm/gsm0808_utils.h b/include/osmocom/gsm/gsm0808_utils.h
index b56e263..c22d0a9 100644
--- a/include/osmocom/gsm/gsm0808_utils.h
+++ b/include/osmocom/gsm/gsm0808_utils.h
@@ -120,6 +120,8 @@
 	return (cause & 0x80) && !(cause & 0x0F);
 }
 
+int gsm0808_get_cipher_reject_cause(const struct tlv_parsed *tp);
+
 /*! \returns 3GPP TS 48.008 3.2.2.49 Current Channel Type 1 from enum gsm_chan_t. */
 static inline uint8_t gsm0808_current_channel_type_1(enum gsm_chan_t type)
 {