diff --git a/tqdm/contrib/concurrent.py b/tqdm/contrib/concurrent.py
index 70fd1f97..ccb5e125 100644
--- a/tqdm/contrib/concurrent.py
+++ b/tqdm/contrib/concurrent.py
@@ -58,7 +58,7 @@ def _executor_map(PoolExecutor, fn, *iterables, **tqdm_kwargs):
     """
     kwargs = tqdm_kwargs.copy()
     if "total" not in kwargs:
-        kwargs["total"] = len(iterables[0])
+        kwargs["total"] = length_hint(iterables[0])
     tqdm_class = kwargs.pop("tqdm_class", tqdm_auto)
     max_workers = kwargs.pop("max_workers", min(32, cpu_count() + 4))
     chunksize = kwargs.pop("chunksize", 1)