diff --git a/rustfmt-config/src/options.rs b/rustfmt-config/src/options.rs
index b6a28b9b58c4..885d89ed752d 100644
--- a/rustfmt-config/src/options.rs
+++ b/rustfmt-config/src/options.rs
@@ -176,7 +176,7 @@ configuration_option_enum! { WriteMode:
     Plain,
     // Outputs a checkstyle XML file.
     Checkstyle,
-    // Output the changed lines
+    // Output the changed lines (for internal value only)
     Modified,
 }