doc update
diff --git a/documentation/pyserial_api.rst b/documentation/pyserial_api.rst
index 1b15762..a3f2ae8 100644
--- a/documentation/pyserial_api.rst
+++ b/documentation/pyserial_api.rst
@@ -139,7 +139,9 @@
In case a write timeout is configured for the port and the time is
exceeded.
- Write the string *data* to the port.
+ Write the bytes *data* to the port. This should be of type ``bytes``
+ (or compatible such as ``bytearray`` or ``memoryview``). Unicode
+ strings must be encoded (e.g. ``'hello'.encode('utf-8'``).
.. versionchanged:: 2.5
Accepts instances of :class:`bytes` and :class:`bytearray` when