diff --git a/app/components/at_mention/at_mention.js b/app/components/at_mention/at_mention.js
index cbf5744e8..f800ef4a2 100644
--- a/app/components/at_mention/at_mention.js
+++ b/app/components/at_mention/at_mention.js
@@ -80,7 +80,7 @@ export default class AtMention extends React.PureComponent {
     };
 
     getUserDetailsFromMentionName(props) {
-        let mentionName = props.mentionName;
+        let mentionName = props.mentionName.toLowerCase();
 
         while (mentionName.length > 0) {
             if (props.usersByUsername.hasOwnProperty(mentionName)) {