diff --git a/openbsc/tests/gbproxy/gbproxy_test.c b/openbsc/tests/gbproxy/gbproxy_test.c
index 769dc67..229d2d4 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.c
+++ b/openbsc/tests/gbproxy/gbproxy_test.c
@@ -116,10 +116,14 @@
 		llist_for_each_entry(tlli_info, &state->enabled_tllis, list) {
 			char mi_buf[200];
 			time_t age = now - tlli_info->timestamp;
-			snprintf(mi_buf, sizeof(mi_buf), "(invalid)");
-			gsm48_mi_to_string(mi_buf, sizeof(mi_buf),
-					   tlli_info->mi_data,
-					   tlli_info->mi_data_len);
+			if (tlli_info->mi_data_len > 0) {
+				snprintf(mi_buf, sizeof(mi_buf), "(invalid)");
+				gsm48_mi_to_string(mi_buf, sizeof(mi_buf),
+						   tlli_info->mi_data,
+						   tlli_info->mi_data_len);
+			} else {
+				snprintf(mi_buf, sizeof(mi_buf), "(none)");
+			}
 			rc = fprintf(stream,
 				     "%*s      TLLI %08x, IMSI %s, AGE %d\n",
 				     indent, "",