diff --git a/scripts/base/protocols/ldap/main.zeek b/scripts/base/protocols/ldap/main.zeek
index 417d6afad0..93c301a65a 100644
--- a/scripts/base/protocols/ldap/main.zeek
+++ b/scripts/base/protocols/ldap/main.zeek
@@ -203,7 +203,7 @@ event LDAP::message(c: connection,
     }
 
     if ( diagnostic_message != "" ) {
-      if ( ! sm?$diagnostic_message && sm$diagnostic_message != diagnostic_message ) {
+      if ( sm?$diagnostic_message && sm$diagnostic_message != diagnostic_message ) {
         Reporter::conn_weird("LDAP_search_diagnostic_message_change", c,
                              fmt("%s: %s -> %s", message_id, sm$diagnostic_message, diagnostic_message), "LDAP");
       }