diff --git a/src/externalldap.js b/src/externalldap.js
index f779b8d54..a527095ef 100644
--- a/src/externalldap.js
+++ b/src/externalldap.js
@@ -42,7 +42,7 @@ function translateUser(ldapConfig, ldapUser) {
 
     // RFC: https://datatracker.ietf.org/doc/html/rfc2798
     return {
-        username: ldapUser[ldapConfig.usernameField],
+        username: ldapUser[ldapConfig.usernameField].toLowerCase(),
         email: ldapUser.mail || ldapUser.mailPrimaryAddress,
         displayName: ldapUser.displayName || ldapUser.cn // user.giveName + ' ' + user.sn
     };
@@ -432,7 +432,7 @@ async function syncGroupUsers(externalLdapConfig, progressCallback) {
 
             debug(`syncGroupUsers: Found member object at ${memberDn} adding to group ${group.name}`);
 
-            const username = result[externalLdapConfig.usernameField];
+            const username = result[externalLdapConfig.usernameField].toLowerCase();
             if (!username) continue;
 
             const [getError, userObject] = await safe(users.getByUsername(username));