diff --git a/hosts/mastodon/default.nix b/hosts/mastodon/default.nix
index 7ffa36da..7b73f44d 100644
--- a/hosts/mastodon/default.nix
+++ b/hosts/mastodon/default.nix
@@ -127,6 +127,8 @@
         LDAP_BASE = "ou=users,dc=c3d2,dc=de";
         LDAP_SEARCH_FILTER = "(&(objectclass=person)(|(%{uid}=%{email})(%{mail}=%{email})))";
         LDAP_UID = "uid";
+        # convert .,- (space) in LDAP usernames to underscore
+        LDAP_UID_CONVERSION_ENABLED = "true";
       };
       localDomain = "c3d2.social";
       otpSecretFile = config.sops.secrets."mastodon/otp-secret".path;