diff --git a/tensorboardX/writer.py b/tensorboardX/writer.py
index d7f2017..c1fbffd 100644
--- a/tensorboardX/writer.py
+++ b/tensorboardX/writer.py
@@ -494,7 +494,7 @@ def add_scalars(
         walltime = time.time() if walltime is None else walltime
         fw_logdir = self._get_file_writer().get_logdir()
         for tag, scalar_value in tag_scalar_dict.items():
-            fw_tag = fw_logdir + "/" + main_tag + "/" + tag
+            fw_tag = os.path.join(str(fw_logdir), main_tag, tag)
             if fw_tag in self.all_writers.keys():
                 fw = self.all_writers[fw_tag]
             else: