diff --git a/include/osmocom/bsc/gsm_data.h b/include/osmocom/bsc/gsm_data.h
index 1d12f3d..8af594f 100644
--- a/include/osmocom/bsc/gsm_data.h
+++ b/include/osmocom/bsc/gsm_data.h
@@ -300,6 +300,14 @@
 	LCHAN_SAPI_S_ERROR,
 };
 
+#define MAX_A5_KEY_LEN	(128/8)
+
+struct gsm_encr {
+	uint8_t alg_id;
+	uint8_t key_len;
+	uint8_t key[MAX_A5_KEY_LEN];
+};
+
 struct gsm_lchan {
 	/* The TS that we're part of */
 	struct gsm_bts_trx_ts *ts;