diff --git a/test/blackbox-tests/test-cases/pkg/ocamlformat/dune b/test/blackbox-tests/test-cases/pkg/ocamlformat/dune
index 133cf19e8d7..d972e95b2c5 100644
--- a/test/blackbox-tests/test-cases/pkg/ocamlformat/dune
+++ b/test/blackbox-tests/test-cases/pkg/ocamlformat/dune
@@ -5,3 +5,7 @@
 (cram
  (deps %{bin:curl})
  (applies_to ocamlformat-e2e))
+
+(cram
+ (deps %{bin:md5sum})
+ (applies_to ocamlformat-patch-extra-files))
diff --git a/test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-patch-extra-files.t b/test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-patch-extra-files.t
new file mode 100644
index 00000000000..79d1ef751c1
--- /dev/null
+++ b/test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-patch-extra-files.t
@@ -0,0 +1,83 @@
+'dune fmt' produce lock files inside "dev-tools.locks/ocamlformat" before it starts building
+ocamlformat and its dependencies during the same run of the "dune fmt" command. The source tree is
+loaded before the lock files are produced, this is why any 'patch' file inside
+'dev-tools.locks/ocmalformat' is not copied inside the 'build' directory when a rule depends on it.
+
+In the case of this issue, there is a rule that depends on an 'patch' file in order to copy the file
+inside '_private/default/..' directory, since the file could not be copied, the rule is not activated.
+So it fails when 'dune' trying to apply the patch. After any follwing run of 'dune fmt', it works
+because the 'patch' file is already present.
+
+  $ . ./helpers.sh
+  $ mkrepo
+
+Make a fake ocamlformat:
+  $ make_fake_ocamlformat "0.1"
+
+  $ cat > patch-for-ocamlformat.patch <<EOF
+  > diff a/ocamlformat.ml b/ocamlformat.ml
+  > --- a/ocamlformat.ml
+  > +++ b/ocamlformat.ml
+  > @@ -1,6 +1,6 @@
+  > -let version = "0.1"
+  > +let version = "0.26.2"
+  >  let () =
+  >    if Sys.file_exists ".ocamlformat-ignore" then
+  >    print_endline "ignoring some files"
+  >  ;;
+  >  let () = print_endline ("formatted with version "^version)
+  > EOF
+
+Make the ocamlformat opam package which uses a patch:
+  $ mkpkg ocamlformat "0.26.2"  <<EOF
+  > build: [
+  >   [
+  >     "dune"
+  >     "build"
+  >     "-p"
+  >     name
+  >     "-j"
+  >     jobs
+  >   ]
+  > ]
+  > extra-files: ["patch-for-ocamlformat.patch" "md5=$(md5sum patch-for-ocamlformat.patch | cut -f1 -d' ')"]
+  > patches: ["patch-for-ocamlformat.patch"]
+  > url {
+  >  src:"file://$PWD/ocamlformat-0.1.tar"
+  >  checksum: [
+  >   "md5=$(md5sum ocamlformat-0.1.tar | cut -f1 -d' ')"
+  >  ]
+  > }
+  > EOF
+  $ mkdir -p mock-opam-repository/packages/ocamlformat/ocamlformat.0.26.2/files/
+  $ cp patch-for-ocamlformat.patch mock-opam-repository/packages/ocamlformat/ocamlformat.0.26.2/files/
+
+Make a project that uses the fake ocamlformat:
+  $ make_project_with_dev_tool_lockdir
+
+First run of 'dune fmt'
+  $ DUNE_CONFIG__LOCK_DEV_TOOL=enabled dune fmt 2>&1 | sed -E 's#.*.sandbox/[^/]+#.sandbox/$SANDBOX#g'
+  Solution for dev-tools.locks/ocamlformat:
+  - ocamlformat.0.26.2
+  Error:
+  .sandbox/$SANDBOX/_private/default/.dev-tool/ocamlformat/ocamlformat/source/patch-for-ocamlformat.patch:
+  No such file or directory
+  -> required by
+     _build/_private/default/.dev-tool/ocamlformat/ocamlformat/target/bin/ocamlformat
+  -> required by _build/default/.formatted/foo.ml
+  -> required by alias .formatted/fmt
+  -> required by alias fmt
+
+The second run will works because the 'patch' is already in the source.
+  $ ls dev-tools.locks/ocamlformat/ocamlformat.files
+  patch-for-ocamlformat.patch
+
+Second run of 'dune fmt'
+  $ DUNE_CONFIG__LOCK_DEV_TOOL=enabled dune fmt
+  File "foo.ml", line 1, characters 0-0:
+  Error: Files _build/default/foo.ml and _build/default/.formatted/foo.ml
+  differ.
+  Promoting _build/default/.formatted/foo.ml to foo.ml.
+  [1]
+  $ cat foo.ml
+  formatted with version 0.26.2