diff --git a/src/tools/compiletest/src/header.rs b/src/tools/compiletest/src/header.rs
index 6bc6e7f597e0..f9013f4b1073 100644
--- a/src/tools/compiletest/src/header.rs
+++ b/src/tools/compiletest/src/header.rs
@@ -125,7 +125,8 @@ pub struct TestProps {
     pub unset_exec_env: Vec<String>,
     // Build documentation for all specified aux-builds as well
     pub build_aux_docs: bool,
-    // Build the documentation for each crate in a unique output directory
+    /// Build the documentation for each crate in a unique output directory.
+    /// Uses <root output directory>/docs/<test name>/doc
     pub unique_doc_out_dir: bool,
     // Flag to force a crate to be built with the host architecture
     pub force_host: bool,