diff --git a/docs/api/chat.mdx b/docs/api/chat.mdx
index aad1261..3d1469f 100644
--- a/docs/api/chat.mdx
+++ b/docs/api/chat.mdx
@@ -1910,11 +1910,6 @@ def map(
         ~~~
     """
     for callback in callbacks:
-        if not asyncio.iscoroutinefunction(callback):
-            raise TypeError(
-                f"Callback '{get_qualified_name(callback)}' must be an async function",
-            )
-
         if allow_duplicates:
             continue
 
@@ -2661,11 +2656,6 @@ def then(
         ~~~
     """
     for callback in callbacks:
-        if not asyncio.iscoroutinefunction(callback):
-            raise TypeError(
-                f"Callback '{get_qualified_name(callback)}' must be an async function",
-            )
-
         if allow_duplicates:
             continue
 
diff --git a/rigging/chat.py b/rigging/chat.py
index 1d944f1..5e5c242 100644
--- a/rigging/chat.py
+++ b/rigging/chat.py
@@ -618,7 +618,7 @@ def __call__(
         self,
         chat: Chat,
         /,
-    ) -> t.Awaitable[Chat | None]: ...
+    ) -> t.Awaitable[Chat | None] | Chat | None: ...
 
 
 @runtime_checkable
@@ -642,7 +642,7 @@ def __call__(
         self,
         chats: list[Chat],
         /,
-    ) -> t.Awaitable[list[Chat]]: ...
+    ) -> t.Awaitable[list[Chat]] | list[Chat]: ...
 
 
 @runtime_checkable
@@ -773,7 +773,9 @@ async def traced_watch_callback(chats: list[Chat]) -> None:
             chat_count=len(chats),
             chat_ids=[str(c.uuid) for c in chats],
         ):
-            await callback(chats)
+            result = callback(chats)
+            if inspect.isawaitable(result):
+                await result
 
     return traced_watch_callback
 
@@ -1100,11 +1102,6 @@ async def process(chat: Chat) -> Chat | None:
             ```
         """
         for callback in callbacks:
-            if not asyncio.iscoroutinefunction(callback):
-                raise TypeError(
-                    f"Callback '{get_qualified_name(callback)}' must be an async function",
-                )
-
             if allow_duplicates:
                 continue
 
@@ -1147,11 +1144,6 @@ async def process(chats: list[Chat]) -> list[Chat]:
             ```
         """
         for callback in callbacks:
-            if not asyncio.iscoroutinefunction(callback):
-                raise TypeError(
-                    f"Callback '{get_qualified_name(callback)}' must be an async function",
-                )
-
             if allow_duplicates:
                 continue
 
@@ -1565,9 +1557,8 @@ async def complete() -> None:
                 exit_stack.push_async_callback(complete)
 
                 result = callback(state.chat)
-
                 if inspect.isawaitable(result):
-                    result = await result  # type: ignore [assignment]
+                    result = await result
 
                 if result is None or isinstance(result, Chat):
                     state.chat = result or state.chat
diff --git a/tests/test_message_slicing.py b/tests/test_message_slicing.py
index fb5718b..9dbff45 100644
--- a/tests/test_message_slicing.py
+++ b/tests/test_message_slicing.py
@@ -953,7 +953,13 @@ def test_slice_with_empty_string_target() -> None:
     """Test marking slice with empty string target."""
     message = Message("assistant", "Some content here")
 
-    slice_obj = message.mark_slice("")
+    # Expect a "Empty string target provided" warning
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        slice_obj = message.mark_slice("")
+        assert len(w) == 1
+        assert issubclass(w[-1].category, MessageWarning)
+        assert "Empty string target provided" in str(w[-1].message)
 
     # Empty string should not create a valid slice
     assert slice_obj is None