diff --git a/openbsc/src/gprs/gprs_gmm.c b/openbsc/src/gprs/gprs_gmm.c
index 3977c66..1e1372c 100644
--- a/openbsc/src/gprs/gprs_gmm.c
+++ b/openbsc/src/gprs/gprs_gmm.c
@@ -70,6 +70,7 @@
 #define GSM0408_T3313_SECS	30	/* waiting for paging response */
 #define GSM0408_T3314_SECS	44	/* force to STBY on expiry, Ready timer */
 #define GSM0408_T3316_SECS	44
+#define GSM0408_MOBILE_REACHABLE_SECS (GSM0408_T3312_SECS + 4 * 60)
 
 /* Section 11.3 / Table 11.2d Timers of Session Management - network side */
 #define GSM0408_T3385_SECS	8	/* wait for ACT PDP CTX REQ */
@@ -140,6 +141,11 @@
 	osmo_timer_del(&mm->timer);
 }
 
+time_t gprs_max_time_to_idle(void)
+{
+	return GSM0408_T3314_SECS + GSM0408_MOBILE_REACHABLE_SECS;
+}
+
 /* Send a message through the underlying layer */
 static int gsm48_gmm_sendmsg(struct msgb *msg, int command,
 			     struct sgsn_mm_ctx *mm)