--- a/pylib/mozreview/mozreview/ldap/__init__.py
+++ b/pylib/mozreview/mozreview/ldap/__init__.py
@@ -138,29 +138,35 @@ def associate_employee_ldap(user, ldap_c
     checked), and associate the user to LDAP.
 
     Raises an exception if no matches or multiple matches were found.
     Returns the found LDAP username, and a boolean indicating if the user
     was updated.
     """
 
     from mozreview.models import get_profile
+    mozreview_profile = get_profile(user)
+
+    # Don't overwrite existing and valid associations.
+    if mozreview_profile.ldap_username and user_exists(
+            mozreview_profile.ldap_username, ldap_connection):
+        return mozreview_profile.ldap_username, False
+
     ldap_users = find_employee_ldap(user.email, ldap_connection)
 
     if not ldap_users:
         raise LDAPAssociationException(
             'Failed to find match for %s' % user.email)
 
     if len(ldap_users) > 1:
         raise LDAPAssociationException(
             'More than one match for %s' % user.email)
 
     ldap_username = ldap_users[0]
     updated = False
-    mozreview_profile = get_profile(user)
     if mozreview_profile.ldap_username != ldap_username:
         if mozreview_profile.ldap_username:
             logging.info("Existing ldap association '%s' replaced by '%s'"
                          % (mozreview_profile.ldap_username, ldap_username))
         else:
             logging.info('Associating user: %s with ldap_username: %s'
                          % (user.email, ldap_username))