diff --git a/kadmin/kadmin.1 b/kadmin/kadmin.1
index 8b9f75e70..6765a546f 100644
--- a/kadmin/kadmin.1
+++ b/kadmin/kadmin.1
@@ -728,7 +728,13 @@ Exits
 This command has the following alias:
 .Nm quit .
 .Ed
-.\".Sh ENVIRONMENT
+.Sh ENVIRONMENT
+.Ev KADMIN_USE_GET_PRINCIPALS ,
+if set to any non-empty value then it uses a slower RPC to list
+principals when talking to a remote
+.Nm kadmind
+server.
+This is useful when the server is an older version of Heimdal.
 .\".Sh FILES
 .\".Sh EXAMPLES
 .\".Sh DIAGNOSTICS