diff --git a/mongoose.c b/mongoose.c
index f2f930a3..1e9cdcfe 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4365,7 +4365,11 @@ static void tx_dhcp_request_sel(struct mg_tcpip_if *ifp, uint32_t ip_req,
                              (ifp->enable_req_sntp ? 1 : 0));
   size_t len = strlen(ifp->dhcp_name);
   size_t olen = 21 + len + extra + 2 + 1;   // Total length of options
-  uint8_t *opts = alloca(olen), *p = opts;  // Allocate options
+  uint8_t opts_maxlen = 21 + sizeof(ifp->dhcp_name) + 2 + 2 + 1;
+  uint8_t opts[opts_maxlen]; // Allocate options (max size possible)
+  uint8_t *p = opts;
+  assert(olen <= sizeof(opts));
+  memset(opts, 0, sizeof(opts));
   *p++ = 53, *p++ = 1, *p++ = 3;            // Type: DHCP request
   *p++ = 54, *p++ = 4, memcpy(p, &ip_srv, 4), p += 4;  // DHCP server ID
   *p++ = 50, *p++ = 4, memcpy(p, &ip_req, 4), p += 4;  // Requested IP
diff --git a/src/net_builtin.c b/src/net_builtin.c
index adfc23bd..1245245a 100644
--- a/src/net_builtin.c
+++ b/src/net_builtin.c
@@ -284,7 +284,11 @@ static void tx_dhcp_request_sel(struct mg_tcpip_if *ifp, uint32_t ip_req,
                              (ifp->enable_req_sntp ? 1 : 0));
   size_t len = strlen(ifp->dhcp_name);
   size_t olen = 21 + len + extra + 2 + 1;   // Total length of options
-  uint8_t *opts = alloca(olen), *p = opts;  // Allocate options
+  uint8_t opts_maxlen = 21 + sizeof(ifp->dhcp_name) + 2 + 2 + 1;
+  uint8_t opts[opts_maxlen]; // Allocate options (max size possible)
+  uint8_t *p = opts;
+  assert(olen <= sizeof(opts));
+  memset(opts, 0, sizeof(opts));
   *p++ = 53, *p++ = 1, *p++ = 3;            // Type: DHCP request
   *p++ = 54, *p++ = 4, memcpy(p, &ip_srv, 4), p += 4;  // DHCP server ID
   *p++ = 50, *p++ = 4, memcpy(p, &ip_req, 4), p += 4;  // Requested IP