diff --git a/src/Tiny_httpd_dir.ml b/src/Tiny_httpd_dir.ml
index c471d25c..748e7abe 100644
--- a/src/Tiny_httpd_dir.ml
+++ b/src/Tiny_httpd_dir.ml
@@ -204,9 +204,10 @@ let add_dir_path ~config ~dir ~prefix server =
              S.Response.make_raw ~code:405 "listing dir not allowed"
         ) else (
           try
-            let bs = Bigstring_unix.with_map_file ~flags:[Open_rdonly] full_path
-                       (fun s -> s)
-            in
+            let fd = Unix.(openfile full_path [O_RDONLY] 0) in
+            let len = stat.Unix.st_size in
+            let bs = Bigstring_unix.map_file_descr fd len in
+            Gc.finalise (fun _ -> Unix.close fd) bs;
             let mime_type =
               if Filename.extension full_path = ".css" then (
                 ["Content-Type", "text/css"]
@@ -224,10 +225,8 @@ let add_dir_path ~config ~dir ~prefix server =
               ~headers:(mime_type@["Etag", mtime_str])
               ~code:200 bs
           with e ->
-            S.Response.fail ~code:500 "error while reading file: %s" (Printexc.to_string e))
-      )
-  ) else (
+            S.Response.fail ~code:500 "error while reading file: %s" (Printexc.to_string e)))) else (
     S.add_route_handler server ~meth:`GET
       S.Route.(exact_path prefix (string @/ return))
            (fun _ _  -> S.Response.make_raw ~code:405 "download not allowed");
-  );
+       );
diff --git a/tests/dl-out.expect b/tests/dl-out.expect
index d0e79081..fb1769c9 100644
--- a/tests/dl-out.expect
+++ b/tests/dl-out.expect
@@ -1,2 +1,5 @@
 serve directory . on http://127.0.0.1:8084
-       0        0 52428800 data2
+        0         0  52428800 data21
+        0         0  52428800 data22
+        0         0  52428800 data23
+        0         0 157286400 total
diff --git a/tests/download_chunked.sh b/tests/download_chunked.sh
index ca70f77b..caa9a8b2 100755
--- a/tests/download_chunked.sh
+++ b/tests/download_chunked.sh
@@ -8,16 +8,16 @@ PID=$!
 sleep 0.1
 
 echo download1 1>&2
-curl -N "http://localhost:${PORT}/foo_50" -o data2 \
+curl -N "http://localhost:${PORT}/foo_50" -o data21 \
   -H 'Tranfer-encoding: chunked'
 
 echo download2 1>&2
-curl -N "http://localhost:${PORT}/foo_50" -o data2 \
+curl -N "http://localhost:${PORT}/foo_50" -o data22 \
   -H 'Tranfer-encoding: chunked'
 
 echo download3 1>&2
-curl -N "http://localhost:${PORT}/foo_50" -o data2 \
+curl -N "http://localhost:${PORT}/foo_50" -o data23 \
   -H 'Tranfer-encoding: chunked'
 
 kill $PID
-wc data2
+wc data21 data22 data23