diff --git a/utils/osmo-aka-verify.c b/utils/osmo-aka-verify.c
index 086add5..bbc65ef 100644
--- a/utils/osmo-aka-verify.c
+++ b/utils/osmo-aka-verify.c
@@ -123,6 +123,7 @@
 	bool opc_is_set = false;
 	bool amf_is_set = false;
 	bool opc_is_op = false;
+	int64_t val64;
 
 	while (1) {
 		int c;
@@ -169,7 +170,8 @@
 			amf_is_set = true;
 			break;
 		case 's':
-			g_sqn = strtoull(optarg, 0, 10);
+			rc = osmo_str_to_int64(&val64, optarg, 10, 0, INT64_MAX);
+			g_sqn = (unsigned long long)val64;
 			sqn_is_set = true;
 			break;
 		case 'r':