diff --git a/src/nvim/api/win_config.c b/src/nvim/api/win_config.c
index f03e6e1eab..33d80246a3 100644
--- a/src/nvim/api/win_config.c
+++ b/src/nvim/api/win_config.c
@@ -235,8 +235,9 @@ Window nvim_open_win(Buffer buffer, Boolean enter, Dict(win_config) *config, Err
 
   win_T *wp = NULL;
   tabpage_T *tp = curtab;
-  win_T *parent = NULL;
-  if (config->win != -1) {
+  assert(curwin != NULL);
+  win_T *parent = config->win == 0 ? curwin : NULL;
+  if (config->win > 0) {
     parent = find_window_by_handle(fconfig.window, err);
     if (!parent) {
       // find_window_by_handle has already set the error
@@ -408,8 +409,8 @@ void nvim_win_set_config(Window window, Dict(win_config) *config, Error *err)
   if (!parse_win_config(win, config, &fconfig, !was_split || to_split, err)) {
     return;
   }
-  win_T *parent = NULL;
-  if (config->win != -1) {
+  win_T *parent = config->win == 0 ? curwin : NULL;
+  if (config->win > 0) {
     parent = find_window_by_handle(fconfig.window, err);
     if (!parent) {
       return;
@@ -1193,8 +1194,6 @@ static bool parse_win_config(win_T *wp, Dict(win_config) *config, WinConfig *fco
                     "non-float with 'win' requires at least 'split' or 'vertical'");
       goto fail;
     }
-  } else {
-    fconfig->window = 0;
   }
 
   if (HAS_KEY_X(config, external)) {
diff --git a/test/functional/ui/float_spec.lua b/test/functional/ui/float_spec.lua
index 0f70b6366e..d2837dcf85 100644
--- a/test/functional/ui/float_spec.lua
+++ b/test/functional/ui/float_spec.lua
@@ -388,7 +388,11 @@ describe('float window', function()
       row = 1,
     })
     eq(1001, api.nvim_win_get_config(winid).win)
+    -- But unrelated config doesn't clear parent win #34286
+    api.nvim_win_set_config(winid, { title = 'foo' })
+    eq(1001, api.nvim_win_get_config(winid).win)
     command('close')
+    api.nvim_win_set_config(winid, { title = 'bar' })
     api.nvim_win_set_config(winid, { relative = 'editor', row = 1, col = 1 })
     eq(nil, api.nvim_win_get_config(winid).win)
   end)