diff --git a/src/libtest/cli.rs b/src/libtest/cli.rs
index 5317063b80d11..aac454c023c80 100644
--- a/src/libtest/cli.rs
+++ b/src/libtest/cli.rs
@@ -213,7 +213,7 @@ macro_rules! unstable_optflag {
         let opt = $matches.opt_present($option_name);
         if !$allow_unstable && opt {
             return Err(format!(
-                "The \"{}\" flag is only accepted on the nightly compiler",
+                "The \"{}\" flag is only accepted on the nightly compiler with -Z unstable-options",
                 $option_name
             ));
         }