diff --git a/src/build_dir.rs b/src/build_dir.rs
index 9ad199f1..26038ed9 100644
--- a/src/build_dir.rs
+++ b/src/build_dir.rs
@@ -103,7 +103,7 @@ fn copy_tree(
     console: &Console,
 ) -> Result<TempDir> {
     let temp_dir = tempfile::Builder::new()
-        .prefix(&name_base)
+        .prefix(name_base)
         .suffix(".tmp")
         .tempdir()
         .context("create temp dir")?;
diff --git a/src/visit.rs b/src/visit.rs
index c0099b09..1046dfe4 100644
--- a/src/visit.rs
+++ b/src/visit.rs
@@ -1,6 +1,7 @@
 // Copyright 2021-2023 Martin Pool
 
-//! Visit the abstract syntax tree and discover things to mutate.
+//! Visit all the files in a source tree, and then the AST of each file,
+//! to discover mutation opportunities.
 //!
 //! Walking the tree starts with some root files known to the build tool:
 //! e.g. for cargo they are identified from the targets. The tree walker then