diff --git a/synapse/http/servlet.py b/synapse/http/servlet.py
index a1e4b88e6..528125e73 100644
--- a/synapse/http/servlet.py
+++ b/synapse/http/servlet.py
@@ -121,16 +121,15 @@ def parse_string(request, name, default=None, required=False,
 
     Args:
         request: the twisted HTTP request.
-        name (bytes/unicode): the name of the query parameter.
-        default (bytes/unicode|None): value to use if the parameter is absent,
+        name (bytes|unicode): the name of the query parameter.
+        default (bytes|unicode|None): value to use if the parameter is absent,
             defaults to None. Must be bytes if encoding is None.
         required (bool): whether to raise a 400 SynapseError if the
             parameter is absent, defaults to False.
-        allowed_values (list[bytes/unicode]): List of allowed values for the
+        allowed_values (list[bytes|unicode]): List of allowed values for the
             string, or None if any value is allowed, defaults to None. Must be
             the same type as name, if given.
-        encoding: The encoding to decode the name to, and decode the string
-            content with.
+        encoding (str|None): The encoding to decode the string content with.
 
     Returns:
         bytes/unicode|None: A string value or the default. Unicode if encoding