diff --git a/streamable/iterators.py b/streamable/iterators.py
index 68e6b1b..74cbb56 100644
--- a/streamable/iterators.py
+++ b/streamable/iterators.py
@@ -680,38 +680,37 @@ def __iter__(self) -> Iterator[Union[T, _RaisingIterator.ExceptionContainer]]:
             element_to_yield: Deque[Union[T, _RaisingIterator.ExceptionContainer]] = (
                 deque(maxlen=1)
             )
-            iterator_to_queue: Deque[Iterator[T]] = deque(maxlen=1)
+            iterator_to_queue: Optional[Iterator[T]] = None
             # wait, queue, yield (FIFO)
             while True:
                 if iterator_and_future_pairs:
                     iterator, future = iterator_and_future_pairs.popleft()
                     try:
                         element_to_yield.append(future.result())
-                        iterator_to_queue.append(iterator)
+                        iterator_to_queue = iterator
                     except StopIteration:
                         pass
                     except Exception as e:
                         element_to_yield.append(_RaisingIterator.ExceptionContainer(e))
-                        iterator_to_queue.append(iterator)
+                        iterator_to_queue = iterator
 
                 # queue tasks up to buffersize
                 while len(iterator_and_future_pairs) < self.buffersize:
-                    if iterator_to_queue:
-                        iterator = iterator_to_queue.pop()
-                    else:
+                    if not iterator_to_queue:
                         try:
                             iterable = next(self.iterables_iterator)
                         except StopIteration:
                             break
                         try:
-                            iterator = wrap_error(iter, StopIteration)(iterable)
+                            iterator_to_queue = iter_wo_stopiteration(iterable)
                         except Exception as e:
                             yield _RaisingIterator.ExceptionContainer(e)
                             continue
                     future = executor.submit(
-                        cast(Callable[[Iterable[T]], T], next), iterator
+                        cast(Callable[[Iterable[T]], T], next), iterator_to_queue
                     )
-                    iterator_and_future_pairs.append((iterator, future))
+                    iterator_and_future_pairs.append((iterator_to_queue, future))
+                    iterator_to_queue = None
                 if element_to_yield:
                     yield element_to_yield.pop()
                 if not iterator_and_future_pairs: