diff --git a/CHANGES.md b/CHANGES.md
index d2176aab12a..9368e4aa6ea 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -5,6 +5,9 @@
   unremovable files would make dune crash when the shared cache is enabled.
   (#8243, fixes #8228, @emillon)
 
+- Fix permission errors when `sendfile` is not available (#8234, fixes #8120,
+  @emillon)
+
 3.9.1 (2023-07-06)
 ------------------
 
diff --git a/otherlibs/stdune/src/io.ml b/otherlibs/stdune/src/io.ml
index d07a8616b1e..48cbc3e09db 100644
--- a/otherlibs/stdune/src/io.ml
+++ b/otherlibs/stdune/src/io.ml
@@ -101,7 +101,7 @@ module Copyfile = struct
     | Linux -> `Sendfile
     | Windows | Other -> `Nothing
 
-  let sendfile =
+  let sendfile_with_fallback =
     let setup_copy ?(chmod = Fun.id) ~src ~dst () =
       match Unix.openfile src [ O_RDONLY ] 0 with
       | exception Unix.Unix_error (Unix.ENOENT, _, _) -> Error `Src_missing
@@ -145,10 +145,15 @@ module Copyfile = struct
       | Error `Src_missing ->
         let message = Printf.sprintf "%s: No such file or directory" src in
         raise (Sys_error message)
-      | Ok (fd_src, fd_dst, src_size) ->
-        Exn.protectx (fd_src, fd_dst, src_size)
-          ~f:(fun (src, dst, src_size) -> sendfile ~src ~dst src_size)
-          ~finally:(fun (src, dst, _) ->
+      | Ok (src, dst, src_size) ->
+        Exn.protect
+          ~f:(fun () ->
+            try sendfile ~src ~dst src_size
+            with Unix.Unix_error (EINVAL, "sendfile", _) ->
+              let ic = Unix.in_channel_of_descr src in
+              let oc = Unix.out_channel_of_descr dst in
+              copy_channels ic oc)
+          ~finally:(fun () ->
             Unix.close src;
             Unix.close dst)
 
@@ -176,11 +181,6 @@ module Copyfile = struct
     Exn.protectx (setup_copy ?chmod ~src ~dst ()) ~finally:close_both
       ~f:(fun (ic, oc) -> copy_channels ic oc)
 
-  let sendfile_with_fallback ?chmod ~src ~dst () =
-    try sendfile ?chmod ~src ~dst ()
-    with Unix.Unix_error (EINVAL, "sendfile", _) ->
-      copy_file_portable ?chmod ~src ~dst ()
-
   let copy_file_best =
     match available with
     | `Sendfile -> sendfile_with_fallback
diff --git a/test/blackbox-tests/test-cases/github8041.t b/test/blackbox-tests/test-cases/github8041.t
index 1276dd4dc12..e26f450dbab 100644
--- a/test/blackbox-tests/test-cases/github8041.t
+++ b/test/blackbox-tests/test-cases/github8041.t
@@ -1,12 +1,14 @@
   $ cat > dune-project << EOF
-  > (lang dune 1.0)
+  > (lang dune 2.4)
   > (package
   >  (name p))
   > EOF
 
   $ cat > dune << EOF
+  > (rule (copy data.txt data2.txt))
+  > 
   > (install
-  >  (files data.txt)
+  >  (files data.txt data2.txt)
   >  (section share))
   > EOF
 
@@ -15,3 +17,6 @@
 If sendfile fails, we should fallback to the portable implementation.
 
   $ strace -e inject=sendfile:error=EINVAL -o /dev/null dune build @install
+
+#8210: data2.txt is copied from readonly-file data.txt (#3092), so it needs to
+be adequately unlinked before starting the fallback.