diff --git a/src/work.rs b/src/work.rs
index efc55f1..6eadd9d 100644
--- a/src/work.rs
+++ b/src/work.rs
@@ -60,18 +60,30 @@ where I: IntoIterator<Item = T>,
     let (tx, rx) = handle::spawn_with_cancel(Default::default(), cancel);
     let renamer = tokio::spawn(async move {
 	use futures::prelude::*;
-	rx.for_each_concurrent(4, |(path, hash)| async move
+	// XXX: Renameing concurrently is dangerous
+	rx.for_each(|(path, hash)| async move
 			       {
 				   match hash {
 				       Ok(hash) => {
-					   let new_name = path.parent().unwrap().join(hash.to_hex_string());
+					   let new_name = {
+					       let name = path.parent().unwrap().join(hash.to_hex_string());
+					       if let Some(ext) = path.extension() {
+						   name.with_extension(ext)
+					       } else {
+						   name
+					       }
+					   };
 					   if let Err(_) = tokio::spawn(async move {
-					       match fs::rename(&path, &new_name).await
-					       {
-						   Ok(_) => println!("[.] {:?} -> {:?}", path, new_name),
-						   Err(err) => println!("[!] {:?}: {}", path, err),
+					       if !new_name.exists() {
+						   match fs::rename(&path, &new_name).await
+						   {
+						       Ok(_) => println!("[.] {:?} -> {:?}", path, new_name),
+						       Err(err) => println!("[!] {:?}: {}", path, err),
+						   }
+					       } else {
+						   eprintln!("[w] file exists {:?}", new_name);
 					       }
-					   }).await {
+					   }).await { //XXX: No need to spawn here at all.
 					       eprintln!("[!] panic: rename");
 					   }
 				       },