diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index 9258d1c..e012079 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -150,6 +150,7 @@
 	u_int8_t sres[4];
 	u_int8_t kc[8];
 };
+#define GSM_KEY_SEQ_INVAL	7	/* GSM 04.08 - 10.5.1.2 */
 
 
 struct gsm_lchan;