diff --git a/src/chat/chat_join.c b/src/chat/chat_join.c
index 926643b5..e67091e8 100644
--- a/src/chat/chat_join.c
+++ b/src/chat/chat_join.c
@@ -104,8 +104,11 @@ static void _keys_free_all(struct UTUN_INSTANCE* inst) {
 int chat_join_serialize_member(const struct join_member_data* m,
                                uint8_t* out, size_t out_sz, size_t* out_len) {
     if (!m || !out || !out_len || !m->x25519 || !m->ed25519) return -1;
-    size_t ul = strnlen(m->userinfo, 255);
-    size_t need = 8 + 32 + 32 + 64 + 8 + 64 + 8 + 1 + ul;
+    size_t ul = strnlen(m->userinfo, sizeof(m->userinfo));
+    if (ul > MS_USERINFO_MAX) {
+        DEBUG_WARN(DEBUG_CATEGORY_MEMBER_SYNC, "chat_join: profile exceeds limit bytes=%zu", ul); return -1;
+    }
+    size_t need = 8 + 32 + 32 + 64 + 8 + 64 + 8 + 2 + ul;
     if (need > out_sz) return -1;
     size_t off = 0;
     memcpy(out + off, &m->node_id, 8); off += 8;
@@ -115,7 +118,7 @@ int chat_join_serialize_member(const struct join_member_data* m,
     memcpy(out + off, &m->join_ts, 8); off += 8;
     if (m->update_sig) memcpy(out + off, m->update_sig, 64); else memset(out + off, 0, 64); off += 64;
     memcpy(out + off, &m->update_ts, 8); off += 8;
-    out[off++] = (uint8_t)ul;
+    out[off++] = (uint8_t)(ul >> 8); out[off++] = (uint8_t)ul;
     if (ul) memcpy(out + off, m->userinfo, ul);
     off += ul;
     *out_len = off;
@@ -123,7 +126,7 @@ int chat_join_serialize_member(const struct join_member_data* m,
 }
 
 int chat_join_parse_member(const uint8_t* data, size_t len, struct join_member_data* m) {
-    if (!data || !m || len < 8 + 32 + 32 + 64 + 8 + 64 + 8 + 1) return -1;
+    if (!data || !m || len < 8 + 32 + 32 + 64 + 8 + 64 + 8 + 2) return -1;
     memset(m, 0, sizeof(*m));
     size_t off = 0;
     memcpy(&m->node_id, data + off, 8); off += 8;
@@ -133,9 +136,10 @@ int chat_join_parse_member(const uint8_t* data, size_t len, struct join_member_d
     memcpy(&m->join_ts, data + off, 8); off += 8;
     m->update_sig = data + off; off += 64;
     memcpy(&m->update_ts, data + off, 8); off += 8;
-    uint8_t ul = data[off++];
-    if (off + ul > len) return -1;
-    if (ul > 255) ul = 255;
+    size_t ul = ((size_t)data[off] << 8) | data[off + 1]; off += 2;
+    if (ul > MS_USERINFO_MAX || off + ul != len || memchr(data + off, 0, ul)) {
+        DEBUG_WARN(DEBUG_CATEGORY_MEMBER_SYNC, "chat_join: invalid profile length bytes=%zu payload=%zu", ul, len); return -1;
+    }
     memcpy(m->userinfo, data + off, ul);
     m->userinfo[ul] = '\0';
     return 0;
diff --git a/src/chat/chat_join.h b/src/chat/chat_join.h
index 0c7ae1d8..c9423ba8 100644
--- a/src/chat/chat_join.h
+++ b/src/chat/chat_join.h
@@ -109,7 +109,7 @@ struct join_member_data {
     uint64_t      join_ts;      /* время подписи вступления, Unix seconds */
     const uint8_t* update_sig;  /* 64, может быть NULL */
     uint64_t      update_ts;    /* версия подписанного блока участника */
-    char          userinfo[256]; /* JSON, null-terminated */
+    char          userinfo[1025]; /* JSON до MS_USERINFO_MAX байт, null-terminated */
 };
 
 /* Сериализовать member-блок (без join_key). Возвращает 0 и *out_len, -1 если не влез. */
diff --git a/tests/test_chat_join.c b/tests/test_chat_join.c
index 2717f368..5f9d4f70 100644
--- a/tests/test_chat_join.c
+++ b/tests/test_chat_join.c
@@ -254,15 +254,15 @@ static void t_serialize_parse(void) {
         if (chat_join_parse_member(buf, 10, &p) == -1) OK(); else FAIL();
     }
 
-    TEST("serialize_member: userinfo up to 255"); {
-        char ui[256]; memset(ui, 'a', 255); ui[255] = '\0';
+    TEST("serialize_member: userinfo up to 1024"); {
+        char ui[1025]; memset(ui, 'a', 1024); ui[1024] = '\0';
         struct join_member_data ml = m; ml.userinfo[0] = '\0';
-        memcpy(ml.userinfo, ui, 256);
-        uint8_t b2[512]; size_t l2 = 0;
+        memcpy(ml.userinfo, ui, sizeof(ui));
+        uint8_t b2[1400]; size_t l2 = 0;
         struct join_member_data p; memset(&p, 0, sizeof(p));
         if (chat_join_serialize_member(&ml, b2, sizeof(b2), &l2) != 0
             || chat_join_parse_member(b2, l2, &p) != 0
-            || strlen(p.userinfo) != 255 || memcmp(p.userinfo, ui, 255) != 0) FAIL();
+            || strlen(p.userinfo) != 1024 || memcmp(p.userinfo, ui, 1024) != 0) FAIL();
         else OK();
     }
 }