diff --git a/source/core/security-ldap-external.txt b/source/core/security-ldap-external.txt
index a49a05c14e5..c1f69ffbe37 100644
--- a/source/core/security-ldap-external.txt
+++ b/source/core/security-ldap-external.txt
@@ -382,7 +382,13 @@ with LDAP authentication and authorization:
 
 .. code-block:: shell
 
-   mongo --username alice@dba.example.com --password "secret123" --authenticationDatabase "$external" --authenticationMechanism "PLAIN"  --host "mongodb.example.com" --port 27017
+   mongo --username alice@dba.example.com --password "secret123" --authenticationDatabase '$external' --authenticationMechanism "PLAIN"  --host "mongodb.example.com" --port 27017
+
+.. important::
+
+   The ``$external`` argument must be placed in single quotes, not
+   double quotes, to prevent the shell from interpreting ``$external``
+   as a variable.
 
 .. _security-ldap-external-roles: