diff --git a/torch/utils/data/datapipes/iter/combining.py b/torch/utils/data/datapipes/iter/combining.py
index ce1a9b379903e..7d26220cdf7e8 100644
--- a/torch/utils/data/datapipes/iter/combining.py
+++ b/torch/utils/data/datapipes/iter/combining.py
@@ -70,7 +70,7 @@ class ForkerIterDataPipe(IterDataPipe):
         num_instances: number of instances of the datapipe to create
         buffer_size: this restricts how far ahead the leading child DataPipe
            can read relative to the slowest child DataPipe.
-           Defaults to ``1000``. Use ``-1`` for the unlimited buffer.
+           Defaults to ``10000``. Use ``None`` for the unlimited buffer.
         copy: copy strategy to use for items yielded by each branch. Supported
             options are ``None`` for no copying, ``"shallow"`` for shallow object
             copies, and ``"deep"`` for deep object copies. Defaults to ``None``.
@@ -94,7 +94,7 @@ def __new__(
         cls,
         datapipe: IterDataPipe,
         num_instances: int,
-        buffer_size: int = 1000,
+        buffer_size: int = 10000,
         copy: Optional[Literal["shallow", "deep"]] = None
     ):
         if num_instances < 1:
@@ -143,7 +143,7 @@ def __init__(
         self,
         datapipe: IterDataPipe,
         num_instances: int,
-        buffer_size: int = 1000,
+        buffer_size: int = 10000,
         copy: Optional[Literal["shallow", "deep"]] = None
     ):
         self.main_datapipe = datapipe
@@ -152,11 +152,7 @@ def __init__(
         self.buffer: Deque = deque()
         self.buffer_size = buffer_size
         if self.buffer_size < 0:
-            warnings.warn(
-                "Unlimited buffer size is set for `fork`, "
-                "please be aware of OOM at random places",
-                UserWarning
-            )
+            raise ValueError("Buffer size needs to be positive or None")
         if copy is None:
             self.copy_fn = _no_op
         elif copy == "shallow":
@@ -206,7 +202,7 @@ def get_next_element_by_instance(self, instance_id: int):
                     if self.slowest_ptr < new_min:
                         self.slowest_ptr = new_min
                         self.buffer.popleft()
-                if self.buffer_size >= 0 and self.leading_ptr > self.buffer_size + self.slowest_ptr:
+                if self.buffer_size is not None and self.leading_ptr > self.buffer_size + self.slowest_ptr:
                     raise BufferError("ForkerIterDataPipe buffer overflow," +
                                       f"buffer size {self.buffer_size} is insufficient.")
 
@@ -360,7 +356,7 @@ class DemultiplexerIterDataPipe(IterDataPipe):
         drop_none: defaults to ``False``, if ``True``, the function will skip over elements classified as ``None``
         buffer_size: this defines the maximum number of inputs that the buffer can hold across all child
             DataPipes while waiting for their values to be yielded.
-            Defaults to ``1000``. Use ``-1`` for the unlimited buffer.
+            Defaults to ``100ß0``. Use ``None`` for the unlimited buffer.
 
     Examples:
         >>> # xdoctest: +REQUIRES(module:torchdata)
@@ -383,7 +379,7 @@ class DemultiplexerIterDataPipe(IterDataPipe):
         [1, 3]
     """
     def __new__(cls, datapipe: IterDataPipe, num_instances: int,
-                classifier_fn: Callable[[T_co], Optional[int]], drop_none: bool = False, buffer_size: int = 1000):
+                classifier_fn: Callable[[T_co], Optional[int]], drop_none: bool = False, buffer_size: int = 10000):
         if num_instances < 1:
             raise ValueError(f"Expected `num_instaces` larger than 0, but {num_instances} is found")
 
@@ -410,11 +406,7 @@ def __init__(self, datapipe: IterDataPipe[T_co], num_instances: int,
         self.num_instances = num_instances
         self.buffer_size = buffer_size
         if self.buffer_size < 0:
-            warnings.warn(
-                "Unlimited buffer size is set for `demux`, "
-                "please be aware of OOM at random places",
-                UserWarning
-            )
+            raise ValueError("Buffer size needs to be positive or None")
         self.current_buffer_usage = 0
         self.child_buffers: List[Deque[T_co]] = [deque() for _ in range(num_instances)]
         self.classifier_fn = classifier_fn
@@ -442,7 +434,7 @@ def _find_next(self, instance_id: int) -> T_co:
                 return value
             self.child_buffers[classification].append(value)
             self.current_buffer_usage += 1
-            if self.buffer_size >= 0 and self.current_buffer_usage > self.buffer_size:
+            if self.buffer_size is not None and self.current_buffer_usage > self.buffer_size:
                 raise BufferError(
                     f"DemultiplexerIterDataPipe buffer overflow, buffer size {self.buffer_size} is insufficient.")