diff --git a/specification/appendices/identifier_grammar.rst b/specification/appendices/identifier_grammar.rst
index d53f61ac9..e85bf4107 100644
--- a/specification/appendices/identifier_grammar.rst
+++ b/specification/appendices/identifier_grammar.rst
@@ -139,7 +139,7 @@ history includes events with a ``sender`` which does not conform. In order to
 handle these rooms successfully, clients and servers MUST accept user IDs with
 localparts from the expanded character set::
 
-  extended_user_id_char = %x21-7E
+  extended_user_id_char = %x21-39 / %x3B-7F  ; all ascii printing chars except :
 
 Mapping from other character sets
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