diff --git a/mongoose.c b/mongoose.c
index 9a842d90..50a27d18 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -8816,11 +8816,12 @@ static void rx_ndp_ra(struct mg_tcpip_if *ifp, struct pkt *pkt) {
         mtu = MG_LOAD_BE32(opts + 4);
         if (mtu < 1280 || mtu > ifp->l2mtu) mtu = 0; // RFC-8200, minimum MTU
       } else if (type == 3 && length >= 32) {
-        // process prefix, 4.6.2
+        // process prefix, 4.6.2, ignore if it smells
         uint8_t pfx_flags = opts[3];  // L=0x80, A=0x40
         uint32_t valid = MG_LOAD_BE32(opts + 4);
         uint32_t pref_lifetime = MG_LOAD_BE32(opts + 8);
         prefix_len = opts[2];
+        if (prefix_len >= 128) break;
         prefix = opts + 16;
 
         // TODO (robertc2000): handle prefix options if necessary
diff --git a/src/net_builtin.c b/src/net_builtin.c
index 414999e1..24c3acf1 100644
--- a/src/net_builtin.c
+++ b/src/net_builtin.c
@@ -991,11 +991,12 @@ static void rx_ndp_ra(struct mg_tcpip_if *ifp, struct pkt *pkt) {
         mtu = MG_LOAD_BE32(opts + 4);
         if (mtu < 1280 || mtu > ifp->l2mtu) mtu = 0; // RFC-8200, minimum MTU
       } else if (type == 3 && length >= 32) {
-        // process prefix, 4.6.2
+        // process prefix, 4.6.2, ignore if it smells
         uint8_t pfx_flags = opts[3];  // L=0x80, A=0x40
         uint32_t valid = MG_LOAD_BE32(opts + 4);
         uint32_t pref_lifetime = MG_LOAD_BE32(opts + 8);
         prefix_len = opts[2];
+        if (prefix_len >= 128) break;
         prefix = opts + 16;
 
         // TODO (robertc2000): handle prefix options if necessary