diff --git a/td/telegram/MessageEntity.cpp b/td/telegram/MessageEntity.cpp
index 0c2469459..79556ac5b 100644
--- a/td/telegram/MessageEntity.cpp
+++ b/td/telegram/MessageEntity.cpp
@@ -1126,7 +1126,8 @@ vector<Slice> find_mentions(Slice str) {
     if (mention.size() >= 5) {
       return false;
     }
-    return get_valid_short_usernames().count(mention) == 0;
+    auto lowered_mention = to_lower(mention);
+    return get_valid_short_usernames().count(lowered_mention) == 0;
   });
   return mentions;
 }
diff --git a/test/message_entities.cpp b/test/message_entities.cpp
index d65bc320f..18d3a3f4c 100644
--- a/test/message_entities.cpp
+++ b/test/message_entities.cpp
@@ -44,8 +44,9 @@ TEST(MessageEntities, mention) {
   check_mention("@abcdefghijklmnopqrstuvwxyz123456", {"@abcdefghijklmnopqrstuvwxyz123456"});
   check_mention("@abcdefghijklmnopqrstuvwxyz1234567", {});
   check_mention("нет@mention", {});
-  check_mention("@ya @gif @wiki @vid @bing @pic @bold @imdb @coub @like @vote @giff @cap ya cap @y @yar @bingg @bin",
-                {"@gif", "@wiki", "@vid", "@bing", "@pic", "@bold", "@imdb", "@coub", "@like", "@vote", "@bingg"});
+  check_mention(
+      "@ya @gif @wiki @vid @bing @pic @bold @imdb @ImDb @coub @like @vote @giff @cap ya cap @y @yar @bingg @bin",
+      {"@gif", "@wiki", "@vid", "@bing", "@pic", "@bold", "@imdb", "@ImDb", "@coub", "@like", "@vote", "@bingg"});
 };
 
 static void check_bot_command(const td::string &str, const td::vector<td::string> &expected) {