diff --git a/src/openvpnserv/interactive.c b/src/openvpnserv/interactive.c
index e64ac30..c6963b3 100644
--- a/src/openvpnserv/interactive.c
+++ b/src/openvpnserv/interactive.c
@@ -1901,7 +1901,9 @@
     if (msg->addr_len > 0)
     {
         /* prepare the comma separated address list */
-        CHAR addrs[max_addrs * 64]; /* 64 is enough for one IPv4/6 address */
+        /* cannot use max_addrs here as that is not considered compile
+         * time constant by all compilers and constexpr is C23 */
+        CHAR addrs[_countof(msg->addr) * 64]; /* 64 is enough for one IPv4/6 address */
         size_t offset = 0;
         for (int i = 0; i < addr_len; ++i)
         {