diff --git a/src/aiogram_input/__init__.py b/src/aiogram_input/__init__.py
index e333a9f..67993be 100644
--- a/src/aiogram_input/__init__.py
+++ b/src/aiogram_input/__init__.py
@@ -1,5 +1,6 @@
 from importlib.metadata import PackageNotFoundError, version
 
+from .middleware import DEFAULT_DATA_KEY
 from .setup import setup_input
 from .storage import InputStorage, MemoryInputStorage
 from .waiter import InputWaiter
@@ -10,6 +11,7 @@
     __version__ = "0.0.0"
 
 __all__ = (
+    "DEFAULT_DATA_KEY",
     "InputStorage",
     "InputWaiter",
     "MemoryInputStorage",
diff --git a/src/aiogram_input/middleware.py b/src/aiogram_input/middleware.py
index b09758d..ec66322 100644
--- a/src/aiogram_input/middleware.py
+++ b/src/aiogram_input/middleware.py
@@ -8,7 +8,7 @@
 from .session import SessionManager
 from .waiter import InputWaiter
 
-HANDLER_DATA_KEY = "input"
+DEFAULT_DATA_KEY = "input"
 
 
 class InputMiddleware(BaseMiddleware):
@@ -18,9 +18,18 @@ class InputMiddleware(BaseMiddleware):
     Register only on Dispatcher so every router shares one waiter instance.
     """
 
-    def __init__(self, session: SessionManager, waiter: InputWaiter) -> None:
+    def __init__(
+        self,
+        session: SessionManager,
+        waiter: InputWaiter,
+        *,
+        data_key: str = DEFAULT_DATA_KEY,
+    ) -> None:
+        if not data_key:
+            raise ValueError("data_key must be a non-empty string")
         self._session = session
         self._waiter = waiter
+        self._data_key = data_key
 
     async def __call__(
         self,
@@ -28,7 +37,7 @@ async def __call__(
         event: TelegramObject,
         data: Dict[str, Any],
     ) -> Any:
-        data[HANDLER_DATA_KEY] = self._waiter
+        data[self._data_key] = self._waiter
         if isinstance(event, Message):
             if await self._session.feed(event):
                 return None
diff --git a/src/aiogram_input/setup.py b/src/aiogram_input/setup.py
index 6158aec..e24cf3b 100644
--- a/src/aiogram_input/setup.py
+++ b/src/aiogram_input/setup.py
@@ -4,7 +4,7 @@
 
 from aiogram import Dispatcher
 
-from .middleware import InputMiddleware
+from .middleware import DEFAULT_DATA_KEY, InputMiddleware
 from .registry import WaitRegistry
 from .session import SessionManager
 from .storage import InputStorage, MemoryInputStorage
@@ -16,13 +16,14 @@ def setup_input(
     /,
     *,
     storage: Optional[InputStorage] = None,
+    data_key: str = DEFAULT_DATA_KEY,
 ) -> InputWaiter:
     """
     Register input waiting once on a Dispatcher.
 
-    Injects ``InputWaiter`` into handler data as ``input`` and consumes matching
-    messages only while a wait is active. Other messages pass through to FSM
-    and normal handlers.
+    Injects ``InputWaiter`` into handler data under ``data_key`` (default:
+    ``"input"``) and consumes matching messages only while a wait is active.
+    Other messages pass through to FSM and normal handlers.
     """
     if not isinstance(dispatcher, Dispatcher):
         raise TypeError(
@@ -33,5 +34,5 @@ def setup_input(
     registry = WaitRegistry()
     session = SessionManager(storage, registry)
     waiter = InputWaiter(session)
-    InputMiddleware(session, waiter).setup(dispatcher)
+    InputMiddleware(session, waiter, data_key=data_key).setup(dispatcher)
     return waiter
diff --git a/tests/test_filters_and_pass_through.py b/tests/test_filters_and_pass_through.py
index a2bd05a..fa34cf2 100644
--- a/tests/test_filters_and_pass_through.py
+++ b/tests/test_filters_and_pass_through.py
@@ -8,7 +8,7 @@
 from aiogram.types import CallbackQuery
 
 from aiogram_input import InputWaiter, setup_input
-from aiogram_input.middleware import HANDLER_DATA_KEY, InputMiddleware
+from aiogram_input.middleware import DEFAULT_DATA_KEY, InputMiddleware
 from aiogram_input.session import SessionManager
 from .helpers import make_message
 
@@ -64,7 +64,7 @@ async def test_non_message_event_passes_through_with_injection() -> None:
 
     async def handler(evt, data):
         seen["event"] = evt
-        seen["input"] = data.get(HANDLER_DATA_KEY)
+        seen["input"] = data.get(DEFAULT_DATA_KEY)
         return "cb"
 
     assert await middleware(handler, event, {}) == "cb"
@@ -83,7 +83,7 @@ async def test_unmatched_message_reaches_handler_fsm_coexistence() -> None:
     async def handler(event, data):
         nonlocal reached
         reached = True
-        assert data[HANDLER_DATA_KEY] is waiter
+        assert data[DEFAULT_DATA_KEY] is waiter
         return "handled"
 
     result = await middleware(handler, make_message(999), {})
diff --git a/tests/test_middleware_di.py b/tests/test_middleware_di.py
index e1586c1..7e498f6 100644
--- a/tests/test_middleware_di.py
+++ b/tests/test_middleware_di.py
@@ -8,7 +8,7 @@
 from aiogram.types import Message
 
 from aiogram_input import InputWaiter, MemoryInputStorage, setup_input
-from aiogram_input.middleware import HANDLER_DATA_KEY, InputMiddleware
+from aiogram_input.middleware import DEFAULT_DATA_KEY, InputMiddleware
 
 
 def _message(chat_id: int) -> Message:
@@ -37,7 +37,7 @@ async def test_middleware_injects_waiter_and_passes_through() -> None:
     async def handler(event, data):
         nonlocal called
         called = True
-        assert data[HANDLER_DATA_KEY] is waiter
+        assert data[DEFAULT_DATA_KEY] is waiter
         return "ok"
 
     result = await middleware(handler, _message(1), {})
@@ -45,6 +45,28 @@ async def handler(event, data):
     assert called is True
 
 
+@pytest.mark.asyncio
+async def test_custom_data_key_avoids_name_collision() -> None:
+    dp = Dispatcher()
+    waiter = setup_input(dp, data_key="aiogram_input")
+    middleware = InputMiddleware(waiter._session, waiter, data_key="aiogram_input")
+
+    async def handler(event, data):
+        assert data["input"] == "user-dep"
+        assert data["aiogram_input"] is waiter
+        return "ok"
+
+    assert await middleware(handler, _message(1), {"input": "user-dep"}) == "ok"
+
+
+@pytest.mark.asyncio
+async def test_empty_data_key_rejected() -> None:
+    dp = Dispatcher()
+    waiter = setup_input(dp)
+    with pytest.raises(ValueError, match="data_key"):
+        InputMiddleware(waiter._session, waiter, data_key="")
+
+
 @pytest.mark.asyncio
 async def test_middleware_consumes_matching_wait() -> None:
     dp = Dispatcher()