diff --git a/src/nvim/tui/tui.c b/src/nvim/tui/tui.c
index 6a6de4c15d..f185afd259 100644
--- a/src/nvim/tui/tui.c
+++ b/src/nvim/tui/tui.c
@@ -79,6 +79,7 @@ struct TUIData {
   Loop *loop;
   unibi_var_t params[9];
   char buf[OUTBUF_SIZE];
+  char *buf_to_flush;  ///< If non-null, flush this instead of buf[].
   size_t bufpos;
   TermInput input;
   uv_loop_t write_loop;
@@ -1892,7 +1893,7 @@ static void unibi_goto(TUIData *tui, int row, int col)
   unibi_out(tui, unibi_cursor_address);
 }
 
-#define UNIBI_OUT(fn) \
+#define UNIBI_OUT(fn, name_fn) \
   do { \
     const char *str = NULL; \
     if (unibi_index >= 0) { \
@@ -1910,11 +1911,14 @@ retry: \
       unibi_format(vars, vars + 26, str, params, out, tui, pad, tui); \
       if (tui->overflow) { \
         tui->bufpos = orig_pos; \
-        /* If orig_pos is 0, there's nothing to flush and retrying won't work. */ \
-        /* TODO(zeertzjq): should this situation still be handled? */ \
         if (orig_pos > 0) { \
           flush_buf(tui); \
+          orig_pos = 0; \
           goto retry; \
+        } else {  /* orig_pos == 0 */ \
+          /* There's nothing to flush and retrying won't work. */ \
+          ELOG("TUI: escape sequence for %s too long", name_fn(unibi_index)); \
+          tui->overflow = false; \
         } \
       } \
       tui->cork = false; \
@@ -1922,11 +1926,15 @@ retry: \
   } while (0)
 static void unibi_out(TUIData *tui, int unibi_index)
 {
-  UNIBI_OUT(unibi_get_str);
+#define UNIBI_NAME_STR(i) unibi_name_str((unsigned)(i))
+  UNIBI_OUT(unibi_get_str, UNIBI_NAME_STR);
+#undef UNIBI_NAME_STR
 }
 static void unibi_out_ext(TUIData *tui, int unibi_index)
 {
-  UNIBI_OUT(unibi_get_ext_str);
+#define UNIBI_GET_EXT_STR_NAME(i) unibi_get_ext_str_name(tui->ut, (unsigned)(i))
+  UNIBI_OUT(unibi_get_ext_str, UNIBI_GET_EXT_STR_NAME);
+#undef UNIBI_GET_EXT_STR_NAME
 }
 #undef UNIBI_OUT
 
@@ -1946,8 +1954,14 @@ static void out(void *ctx, const char *str, size_t len)
       return;
     }
     flush_buf(tui);
+    if (len > sizeof(tui->buf)) {
+      // Don't use tui->buf[] when the string to output is too long. #30794
+      tui->buf_to_flush = (char *)str;
+      tui->bufpos = len;
+      flush_buf(tui);
+      return;
+    }
   }
-  // TODO(zeertzjq): handle string longer than buffer size? #30794
 
   memcpy(tui->buf + tui->bufpos, str, len);
   tui->bufpos += len;
@@ -2635,7 +2649,7 @@ static void flush_buf(TUIData *tui)
   bufs[0].base = pre;
   bufs[0].len = UV_BUF_LEN(flush_buf_start(tui, pre, sizeof(pre)));
 
-  bufs[1].base = tui->buf;
+  bufs[1].base = tui->buf_to_flush != NULL ? tui->buf_to_flush : tui->buf;
   bufs[1].len = UV_BUF_LEN(tui->bufpos);
 
   bufs[2].base = post;
@@ -2653,6 +2667,7 @@ static void flush_buf(TUIData *tui)
     }
     uv_run(&tui->write_loop, UV_RUN_DEFAULT);
   }
+  tui->buf_to_flush = NULL;
   tui->bufpos = 0;
   tui->overflow = false;
 }
diff --git a/test/functional/terminal/tui_spec.lua b/test/functional/terminal/tui_spec.lua
index 2b5f455c85..618f779b70 100644
--- a/test/functional/terminal/tui_spec.lua
+++ b/test/functional/terminal/tui_spec.lua
@@ -2297,8 +2297,8 @@ describe('TUI', function()
     ]])
     child_exec_lua([[
       vim.api.nvim_buf_set_lines(0, 0, 0, true, {'Hello'})
-      local ns = vim.api.nvim_create_namespace('test')
-      vim.api.nvim_buf_set_extmark(0, ns, 0, 1, {
+      _G.NS = vim.api.nvim_create_namespace('test')
+      vim.api.nvim_buf_set_extmark(0, _G.NS, 0, 1, {
         end_col = 3,
         url = 'https://example.com',
       })
@@ -2306,6 +2306,19 @@ describe('TUI', function()
     retry(nil, 1000, function()
       eq({ { id = 0xE1EA0000, url = 'https://example.com' } }, exec_lua([[return _G.urls]]))
     end)
+    -- No crash with very long URL #30794
+    child_exec_lua([[
+      vim.api.nvim_buf_set_extmark(0, _G.NS, 0, 3, {
+        end_col = 5,
+        url = 'https://example.com/' .. ('a'):rep(65536),
+      })
+    ]])
+    retry(nil, nil, function()
+      eq({
+        { id = 0xE1EA0000, url = 'https://example.com' },
+        { id = 0xE1EA0001, url = 'https://example.com/' .. ('a'):rep(65536) },
+      }, exec_lua([[return _G.urls]]))
+    end)
   end)
 
   it('TermResponse works with vim.wait() from another autocommand #32706', function()
@@ -3708,6 +3721,44 @@ describe('TUI client', function()
     end
   end)
 
+  it('does not crash or hang with a very long title', function()
+    local server, _, screen_client = start_headless_server_and_client()
+
+    local server_exec_lua = tt.make_lua_executor(server)
+    if not server_exec_lua('return pcall(require, "ffi")') then
+      pending('missing LuaJIT FFI')
+    end
+
+    local bufname = api.nvim_buf_get_name(0)
+    -- Normally a title cannot be longer than the 65535-byte buffer as maketitle()
+    -- limits it length. Use FFI to send a very long title directly.
+    server_exec_lua([=[
+      local ffi = require('ffi')
+      local cstr = ffi.typeof('char[?]')
+      local function to_cstr(string)
+        return cstr(#string + 1, string)
+      end
+
+      ffi.cdef([[
+        typedef struct { char *data; size_t size; } String;
+        void ui_call_set_title(String title);
+      ]])
+
+      local len = 65536
+      local title = ffi.new('String', { data = to_cstr(('a'):rep(len)), size = len })
+      ffi.C.ui_call_set_title(title)
+    ]=])
+    screen_client:expect_unchanged()
+    assert_log('TUI: escape sequence for ext%.set_title too long', testlog)
+    eq(bufname, api.nvim_buf_get_var(0, 'term_title'))
+
+    -- Following escape sequences are not affected.
+    server:request('nvim_set_option_value', 'title', true, {})
+    retry(nil, nil, function()
+      eq('[No Name] + - Nvim', api.nvim_buf_get_var(0, 'term_title'))
+    end)
+  end)
+
   it('throws error when no server exists', function()
     clear()
     local screen = tt.setup_child_nvim({