diff --git a/openbsc/src/gprs/gtphub_ares.c b/openbsc/src/gprs/gtphub_ares.c
index 947f2dd..667013b 100644
--- a/openbsc/src/gprs/gtphub_ares.c
+++ b/openbsc/src/gprs/gtphub_ares.c
@@ -55,7 +55,7 @@
 
 	struct gtphub *hub;
 
-	char imsi_str[GSM_IMSI_LENGTH];
+	char imsi_str[GSM23003_IMSI_MAX_DIGITS+1];
 	char apn_ni_str[GSM_APN_LENGTH];
 	char apn_oi_str[GSM_APN_LENGTH];
 	int have_3dig_mnc;