diff --git a/telethon/extensions/html.py b/telethon/extensions/html.py
index e950900d..8a397336 100644
--- a/telethon/extensions/html.py
+++ b/telethon/extensions/html.py
@@ -9,8 +9,8 @@ from html.parser import HTMLParser
 from ..tl.types import (
     MessageEntityBold, MessageEntityItalic, MessageEntityCode,
     MessageEntityPre, MessageEntityEmail, MessageEntityUrl,
-    MessageEntityTextUrl,
-    MessageEntityMentionName)
+    MessageEntityTextUrl, MessageEntityMentionName
+    )
 
 
 # Helpers from markdown.py
@@ -179,7 +179,7 @@ def unparse(text, entities):
             html.append('<a href="{}">{}</a>'
                         .format(escape(entity.url), entity_text))
         elif entity_type == MessageEntityMentionName:
-            html.append('<a href="{}">{}</a>'
+            html.append('<a href="tg://user?id={}">{}</a>'
                         .format(entity.user_id, entity_text))
         else:
             skip_entity = True
diff --git a/telethon/extensions/markdown.py b/telethon/extensions/markdown.py
index 2560554a..cab1d6a1 100644
--- a/telethon/extensions/markdown.py
+++ b/telethon/extensions/markdown.py
@@ -9,8 +9,8 @@ from ..helpers import add_surrogate, del_surrogate
 from ..tl import TLObject
 from ..tl.types import (
     MessageEntityBold, MessageEntityItalic, MessageEntityCode,
-    MessageEntityPre, MessageEntityTextUrl,
-    MessageEntityMentionName)
+    MessageEntityPre, MessageEntityTextUrl, MessageEntityMentionName
+    )
 
 DEFAULT_DELIMITERS = {
     '**': MessageEntityBold,
@@ -120,9 +120,9 @@ def parse(message, delimiters=None, url_re=None):
     # If this is the case, we want to insert the delimiter character back.
     if current is not None:
         message = (
-                message[:current.offset]
-                + end_delimiter
-                + message[current.offset:]
+            message[:current.offset]
+            + end_delimiter
+            + message[current.offset:]
         )
 
     return del_surrogate(message), result
@@ -163,12 +163,11 @@ def unparse(text, entities, delimiters=None, url_fmt=None):
             text = text[:s] + delimiter + text[s:e] + delimiter + text[e:]
         elif isinstance(entity, MessageEntityTextUrl) and url_fmt:
             text = (
-                    text[:s] +
-                    add_surrogate(url_fmt.format(text[s:e], entity.url)) +
-                    text[e:]
+                text[:s] +
+                add_surrogate(url_fmt.format(text[s:e], entity.url)) +
+                text[e:]
             )
         elif isinstance(entity, MessageEntityMentionName):
-            text = text[:entity.offset] + "[{}](tg://user?id={})".format(
-                text[entity.offset:entity.offset + entity.length], entity.user_id) + text[
-                                                                                     entity.offset + entity.length:]
+            text = text[:s] + "[{}](tg://user?id={})".format(
+                text[s:e], entity.user_id) + text[e:]
     return del_surrogate(text)