diff --git a/.github/workflows/workflow.yml b/.github/workflows/workflow.yml
index 4a124edfa28..4dbd2e88a06 100644
--- a/.github/workflows/workflow.yml
+++ b/.github/workflows/workflow.yml
@@ -168,22 +168,22 @@ jobs:
             os: ubuntu-latest
           # OCaml 5:
           ## ubuntu (x86)
-          - ocaml-compiler: 5.3.x
+          - ocaml-compiler: 5.4.x
             os: ubuntu-latest
             run_tests: true
           ## macos (Apple Silicon)
-          - ocaml-compiler: 5.3.x
+          - ocaml-compiler: 5.4.x
             os: macos-latest
             run_tests: true
           ## macos (x86)
           - ocaml-compiler: 5.4.x
             os: macos-15-intel
           ## MSVC
-          - ocaml-compiler: ocaml-compiler.5.3.0,system-msvc
+          - ocaml-compiler: ocaml-compiler.5.4.0,system-msvc
             os: windows-latest
             run_tests: true
           ## mingw
-          - ocaml-compiler: ocaml-base-compiler.5.3.0,system-mingw
+          - ocaml-compiler: ocaml-base-compiler.5.4.0,system-mingw
             os: windows-latest
             run_tests: true
           # OCaml 4:
diff --git a/Makefile b/Makefile
index e7254ed0c49..e4a13dcc2b1 100644
--- a/Makefile
+++ b/Makefile
@@ -12,7 +12,7 @@ DEV_DEPS := \
 core_bench \
 patdiff
 
-TEST_OCAMLVERSION := 5.3.0
+TEST_OCAMLVERSION := 5.4.0
 # When updating this version, don't forget to also bump the number in the docs.
 
 -include Makefile.dev
@@ -109,9 +109,6 @@ test-melange: $(BIN)
 test-all: $(BIN)
 	$(BIN) build @runtest @runtest-js @runtest-coq @runtest-melange
 
-test-all-sans-melange: $(BIN)
-	$(BIN) build @runtest @runtest-js @runtest-coq
-
 test-ox: $(BIN)
 	$(BIN) runtest test/blackbox-tests/test-cases/oxcaml
 
diff --git a/doc/hacking.rst b/doc/hacking.rst
index 732d1bf3305..7a522989e4f 100644
--- a/doc/hacking.rst
+++ b/doc/hacking.rst
@@ -54,10 +54,10 @@ Here are the most common commands you'll be running:
    $ ./dune.exe build @foo
 
 
-Note that tests are currently written for version 5.3.0 of the OCaml compiler.
+Note that tests are currently written for version 5.4.0 of the OCaml compiler.
 Some tests depend on the specific wording of compilation errors which can change
 between compiler versions, so to reliably run the tests make sure that
-``ocaml.5.3.0`` is installed. The ``TEST_OCAMLVERSION`` in the ``Makefile`` at
+``ocaml.5.4.0`` is installed. The ``TEST_OCAMLVERSION`` in the ``Makefile`` at
 the root of the Dune repo contains the current compiler version for which tests
 are written.
 
diff --git a/doc/tutorials/developing-with-dune/introduction.md b/doc/tutorials/developing-with-dune/introduction.md
index c2c97b287f1..2d43ae0b163 100644
--- a/doc/tutorials/developing-with-dune/introduction.md
+++ b/doc/tutorials/developing-with-dune/introduction.md
@@ -44,7 +44,7 @@ Let's create a local switch: `cd` to this directory and run the following comman
 This can take a few minutes.
 
 ```sh
-opam switch create ./ 5.3.0
+opam switch create ./ 5.4.0
 ```
 
 This command has created a directory named `_opam` in the current directory.
diff --git a/dune.opam b/dune.opam
index 1bb875c04c8..080c2561116 100644
--- a/dune.opam
+++ b/dune.opam
@@ -59,7 +59,7 @@ depends: [
   "ppx_expect" { with-dev-setup & >= "v0.17" & os != "win32" }
   "spawn" { with-dev-setup }
   "ppx_inline_test" { with-dev-setup & os != "win32" }
-  "ppxlib" { with-dev-setup & >= "0.35.0" & os != "win32" }
+  "ppxlib" { with-dev-setup & >= "0.37.0" & os != "win32" }
   "ctypes" { with-dev-setup & os != "win32" }
   "utop" { with-dev-setup & >= "2.6.0" & os != "win32" }
   "melange" { with-dev-setup & >= "5.1.0-51" & os != "win32" }
diff --git a/dune.opam.template b/dune.opam.template
index 68076eaf3a3..a3796ffbaef 100644
--- a/dune.opam.template
+++ b/dune.opam.template
@@ -20,7 +20,7 @@ depends: [
   "ppx_expect" { with-dev-setup & >= "v0.17" & os != "win32" }
   "spawn" { with-dev-setup }
   "ppx_inline_test" { with-dev-setup & os != "win32" }
-  "ppxlib" { with-dev-setup & >= "0.35.0" & os != "win32" }
+  "ppxlib" { with-dev-setup & >= "0.37.0" & os != "win32" }
   "ctypes" { with-dev-setup & os != "win32" }
   "utop" { with-dev-setup & >= "2.6.0" & os != "win32" }
   "melange" { with-dev-setup & >= "5.1.0-51" & os != "win32" }
diff --git a/flake.lock b/flake.lock
index dbe112866d0..d90b6ef9a16 100644
--- a/flake.lock
+++ b/flake.lock
@@ -44,16 +44,16 @@
         ]
       },
       "locked": {
-        "lastModified": 1742771785,
-        "narHash": "sha256-Ihd2b1B/GnRTd0yk63kQ3ryLhgT3hp+Md0BYwOKP+YA=",
+        "lastModified": 1762666707,
+        "narHash": "sha256-USvFyipdEedaBan3H8X1NxfuQi0IDYal5PdsCwmN2Q4=",
         "owner": "melange-re",
         "repo": "melange",
-        "rev": "2432b02d9c1990ae62fd44fad8bb53ea35b1e6b0",
+        "rev": "7b51f143b537076f1ad694464ca2a1102cd23287",
         "type": "github"
       },
       "original": {
         "owner": "melange-re",
-        "ref": "refs/tags/5.1.0-53",
+        "ref": "refs/tags/6.0.0-54",
         "repo": "melange",
         "type": "github"
       }
@@ -66,15 +66,16 @@
         ]
       },
       "locked": {
-        "lastModified": 1742165088,
-        "narHash": "sha256-N5IZA13/RAd6uYJEn12UlfPpPxyBOuVw4am0qadtUms=",
+        "lastModified": 1760240634,
+        "narHash": "sha256-cmPZs92Vva6X06E8MreMVn6Yu5gqZtAYLJRweTEWwRY=",
         "owner": "melange-re",
         "repo": "melange-compiler-libs",
-        "rev": "e914cab0ec7d53130d5f1e283283628c98a3583c",
+        "rev": "b8d6659bfe3045938afa83f37b7c357c052d10c7",
         "type": "github"
       },
       "original": {
         "owner": "melange-re",
+        "ref": "5.4",
         "repo": "melange-compiler-libs",
         "type": "github"
       }
@@ -102,11 +103,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1752012998,
-        "narHash": "sha256-Q82Ms+FQmgOBkdoSVm+FBpuFoeUAffNerR5yVV7SgT8=",
+        "lastModified": 1762156382,
+        "narHash": "sha256-Yg7Ag7ov5+36jEFC1DaZh/12SEXo6OO3/8rqADRxiqs=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "2a2130494ad647f953593c4e84ea4df839fbd68c",
+        "rev": "7241bcbb4f099a66aafca120d37c65e8dda32717",
         "type": "github"
       },
       "original": {
@@ -116,6 +117,22 @@
         "type": "github"
       }
     },
+    "nixpkgs-old": {
+      "locked": {
+        "lastModified": 1746662029,
+        "narHash": "sha256-2lFR2IQHaaUA5X2JMzQ3SGkj5IXFU/ztqpKD4I6vWCw=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "7f50d4b33363d3948543f6a02b90a2c66852a453",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "7f50d4b33363d3948543f6a02b90a2c66852a453",
+        "type": "github"
+      }
+    },
     "ocaml-overlays": {
       "inputs": {
         "nixpkgs": [
@@ -123,11 +140,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1752292614,
-        "narHash": "sha256-PwW/5J+SslGqkaCEad/1fvbTgPw2eI2UJkjStmGSChI=",
+        "lastModified": 1762273825,
+        "narHash": "sha256-jn3EGl4vV/fvBkEmeqsrArZX6PA/uyOhJSKw+Y9rj7I=",
         "owner": "nix-ocaml",
         "repo": "nix-overlays",
-        "rev": "fbbcd2e563cf33e4a4fdbac4395e7276a506ef09",
+        "rev": "e0ec05d668a5d5463b0ca981aa481545af494eb1",
         "type": "github"
       },
       "original": {
@@ -145,11 +162,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1760541218,
-        "narHash": "sha256-eZ2Nx8eXmiTurtJVBlC+MU45N6qFF76LDAa/aum4ZTk=",
+        "lastModified": 1762278632,
+        "narHash": "sha256-bnGCcvEF9ZEsgDSCEgXeHGl/TDL4oxxb+G8/bWp7FNI=",
         "owner": "oxcaml",
         "repo": "oxcaml",
-        "rev": "eea9697287f10719188cfd82d667caaeba346e87",
+        "rev": "10dd7883b15da7a0b3ea9729e95af3fbc360fa0d",
         "type": "github"
       },
       "original": {
@@ -161,11 +178,11 @@
     "oxcaml-opam-repository": {
       "flake": false,
       "locked": {
-        "lastModified": 1760195033,
-        "narHash": "sha256-qWWJ4WiV3hnOw4dFUq363BVejLwkxTk6OaZHUSkHylg=",
+        "lastModified": 1761753924,
+        "narHash": "sha256-g7wbVoC4f2B6khTQn3S6AORitobXt9OnDAI+vIQioLU=",
         "owner": "oxcaml",
         "repo": "opam-repository",
-        "rev": "eeedfd918e54a8741d26af1a4ff2991b21c1045f",
+        "rev": "a1ea0d33dd5662b89183f751c3fec566d7860b75",
         "type": "github"
       },
       "original": {
@@ -179,6 +196,7 @@
         "flake-utils": "flake-utils",
         "melange": "melange",
         "nixpkgs": "nixpkgs",
+        "nixpkgs-old": "nixpkgs-old",
         "ocaml-overlays": "ocaml-overlays",
         "oxcaml": "oxcaml",
         "oxcaml-opam-repository": "oxcaml-opam-repository"
diff --git a/flake.nix b/flake.nix
index bd035e521a1..6016fd4cfe3 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,9 +1,10 @@
 {
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    nixpkgs-old.url = "github:nixos/nixpkgs/7f50d4b33363d3948543f6a02b90a2c66852a453";
     flake-utils.url = "github:numtide/flake-utils";
     melange = {
-      url = "github:melange-re/melange/refs/tags/5.1.0-53";
+      url = "github:melange-re/melange/refs/tags/6.0.0-54";
       inputs.nixpkgs.follows = "nixpkgs";
     };
     ocaml-overlays = {
@@ -24,6 +25,7 @@
       self,
       flake-utils,
       nixpkgs,
+      nixpkgs-old,
       melange,
       ocaml-overlays,
       oxcaml,
@@ -35,7 +37,7 @@
         pkgs = nixpkgs.legacyPackages.${system}.appendOverlays [
           ocaml-overlays.overlays.default
           (self: super: {
-            ocamlPackages = super.ocaml-ng.ocamlPackages_5_3.overrideScope (
+            ocamlPackages = super.ocaml-ng.ocamlPackages_5_4.overrideScope (
               oself: osuper: {
                 mdx = osuper.mdx.override {
                   logs = oself.logs;
@@ -63,8 +65,13 @@
           oxcamlOpamRepo = oxcaml-opam-repository;
         };
 
+        # Older nixpkgs for OCaml 4.02 support
+        pkgs-old = nixpkgs-old.legacyPackages.${system}.appendOverlays [
+          ocaml-overlays.overlays.default
+        ];
+
         dune-static-overlay = self: super: {
-          ocamlPackages = super.ocaml-ng.ocamlPackages_5_3.overrideScope (
+          ocamlPackages = super.ocaml-ng.ocamlPackages_5_4.overrideScope (
             oself: osuper: {
               dune_3 = osuper.dune_3.overrideAttrs (a: {
                 src = ./.;
@@ -91,19 +98,16 @@
 
         ocamlformat =
           let
-            ocamlformat_version =
-              let
-                lists = pkgs.lib.lists;
-                strings = pkgs.lib.strings;
-                ocamlformat_config = strings.splitString "\n" (builtins.readFile ./.ocamlformat);
-                prefix = "version=";
-                ocamlformat_version_pred = line: strings.hasPrefix prefix line;
-                version_line = lists.findFirst ocamlformat_version_pred "not_found" ocamlformat_config;
-                version = strings.removePrefix prefix version_line;
-              in
-              builtins.replaceStrings [ "." ] [ "_" ] version;
+            lists = pkgs.lib.lists;
+            strings = pkgs.lib.strings;
+            ocamlformat_config = strings.splitString "\n" (builtins.readFile ./.ocamlformat);
+            prefix = "version=";
+            ocamlformat_version_pred = line: strings.hasPrefix prefix line;
+            version_line = lists.findFirst ocamlformat_version_pred "not_found" ocamlformat_config;
+            version_string = strings.removePrefix prefix version_line;
+            ocamlformat_attr = builtins.replaceStrings [ "." ] [ "_" ] version_string;
           in
-          builtins.getAttr ("ocamlformat_" + ocamlformat_version) pkgs;
+          builtins.getAttr ("ocamlformat_" + ocamlformat_attr) nixpkgs.legacyPackages.${system};
 
         testBuildInputs =
           with pkgs;
@@ -287,11 +291,11 @@
             fmt = pkgs.mkShell {
               inherit INSIDE_NIX;
               nativeBuildInputs = [ ocamlformat ];
-              # re shouldn't be needed. this is an issue with the fmt rules
               inputsFrom = [
                 pkgs.dune_3
               ];
               buildInputs = with pkgs.ocamlPackages; [
+                # These shouldn't be needed. this is an issue with the fmt rules
                 csexp
                 pp
                 re
@@ -355,9 +359,9 @@
 
             bootstrap-check = pkgs.mkShell {
               inherit INSIDE_NIX;
-              buildInputs = with pkgs; [
-                gnumake
-                ocaml-ng.ocamlPackages_4_02.ocaml
+              buildInputs = [
+                pkgs.gnumake
+                pkgs-old.ocaml-ng.ocamlPackages_4_02.ocaml
               ];
               meta.description = ''
                 Provides a minimal shell environment with OCaml 4.02 in order
@@ -367,9 +371,9 @@
 
             bootstrap-check_4_08 = pkgs.mkShell {
               inherit INSIDE_NIX;
-              buildInputs = with pkgs; [
-                gnumake
-                ocaml-ng.ocamlPackages_4_08.ocaml
+              buildInputs = [
+                pkgs.gnumake
+                pkgs-old.ocaml-ng.ocamlPackages_4_08.ocaml
               ];
               meta.description = ''
                 Provides a minimal shell environment with OCaml 4.08 in order
diff --git a/src/dune_rules/module.ml b/src/dune_rules/module.ml
index ada39d63387..ebaf4efbcc7 100644
--- a/src/dune_rules/module.ml
+++ b/src/dune_rules/module.ml
@@ -336,6 +336,15 @@ let sources_without_pp t =
     ~f:(Option.map ~f:(fun (x : File.t) -> x.original_path))
 ;;
 
+let source_without_pp ~ml_kind t =
+  let source =
+    match (ml_kind : Ml_kind.t) with
+    | Impl -> t.source.files.impl
+    | Intf -> t.source.files.intf
+  in
+  Option.map source ~f:(fun (x : File.t) -> x.original_path)
+;;
+
 module Obj_map = struct
   include Map.Make (struct
       type nonrec t = t
diff --git a/src/dune_rules/module.mli b/src/dune_rules/module.mli
index b95cf62cbc6..fe095bb12e5 100644
--- a/src/dune_rules/module.mli
+++ b/src/dune_rules/module.mli
@@ -88,6 +88,7 @@ end
 
 val sources : t -> Path.t list
 val sources_without_pp : t -> Path.t list
+val source_without_pp : ml_kind:Ml_kind.t -> t -> Path.t option
 val visibility : t -> Visibility.t
 val encode : t -> src_dir:Path.t -> Dune_lang.t list
 val decode : src_dir:Path.t -> t Dune_lang.Decoder.t
diff --git a/src/dune_rules/module_compilation.ml b/src/dune_rules/module_compilation.ml
index f59df0fb085..b5d42b02eae 100644
--- a/src/dune_rules/module_compilation.ml
+++ b/src/dune_rules/module_compilation.ml
@@ -158,6 +158,7 @@ let build_cm
    let* compiler = compiler in
    let ml_kind = Lib_mode.Cm_kind.source cm_kind in
    let+ src = Module.file m ~ml_kind in
+   let original = Module.source_without_pp m ~ml_kind in
    let dst = Obj_dir.Module.cm_file_exn obj_dir m ~kind:cm_kind in
    let obj =
      Obj_dir.Module.obj_file obj_dir m ~kind:(Ocaml Cmx) ~ext:ocaml.lib_config.ext_obj
@@ -324,6 +325,7 @@ let build_cm
             ; A "-c"
             ; Command.Ml_kind.flag ml_kind
             ; Dep src
+            ; Hidden_deps (Dep.Set.of_files (Option.to_list original))
             ; other_targets
             ]
       >>| Action.Full.add_sandbox sandbox))
diff --git a/test/blackbox-tests/test-cases/hidden-deps-supported.t/run.t b/test/blackbox-tests/test-cases/hidden-deps-supported.t/run.t
index 667a3058512..96fce95e31b 100644
--- a/test/blackbox-tests/test-cases/hidden-deps-supported.t/run.t
+++ b/test/blackbox-tests/test-cases/hidden-deps-supported.t/run.t
@@ -49,7 +49,7 @@ Test transitive deps can not be directly accessed, both for compiler versions su
   > EOF
 
   $ dune build ./runf.exe 2>&1 | grep -v ocamlc
-  File "runf.ml", line 1, characters 16-21:
+  File "runf.ml", line 1, characters 16-19:
   1 | let _ = Bar.y + Foo.v
-                      ^^^^^
+                      ^^^
   Error: Unbound module Foo
diff --git a/test/blackbox-tests/test-cases/include-qualified/invalid-deps/toplevel-lib-interface.t b/test/blackbox-tests/test-cases/include-qualified/invalid-deps/toplevel-lib-interface.t
index 35fd7cb4187..3b146f66b00 100644
--- a/test/blackbox-tests/test-cases/include-qualified/invalid-deps/toplevel-lib-interface.t
+++ b/test/blackbox-tests/test-cases/include-qualified/invalid-deps/toplevel-lib-interface.t
@@ -17,8 +17,8 @@ We should forbid lib interfaces modules from depending on themselves:
   $ touch bar.ml
 
   $ dune build @check
-  File "foo.ml", line 1, characters 9-14:
+  File "foo.ml", line 1, characters 9-12:
   1 | let () = Foo.f ()
-               ^^^^^
+               ^^^
   Error: Unbound module Foo
   [1]
diff --git a/test/blackbox-tests/test-cases/include-qualified/ocamldep-regression.t b/test/blackbox-tests/test-cases/include-qualified/ocamldep-regression.t
index 7d64b6ff027..502d4b9b04f 100644
--- a/test/blackbox-tests/test-cases/include-qualified/ocamldep-regression.t
+++ b/test/blackbox-tests/test-cases/include-qualified/ocamldep-regression.t
@@ -17,9 +17,9 @@ We should forbid lib interfaces modules from depending on themselves:
   $ touch bar.ml
 
   $ dune build @check
-  File "foo.ml", line 1, characters 9-14:
+  File "foo.ml", line 1, characters 9-12:
   1 | let () = Foo.f ()
-               ^^^^^
+               ^^^
   Error: Unbound module Foo
   [1]
 
diff --git a/test/blackbox-tests/test-cases/include-subdirs/stop-at-project-root.t b/test/blackbox-tests/test-cases/include-subdirs/stop-at-project-root.t
index b18c1711016..2efe9ea984d 100644
--- a/test/blackbox-tests/test-cases/include-subdirs/stop-at-project-root.t
+++ b/test/blackbox-tests/test-cases/include-subdirs/stop-at-project-root.t
@@ -32,8 +32,8 @@ Doesn't work with when we make [subproj] a separate project with a dune-project
 file, since include_subdirs is stopped.
 
   $ dune exec ./foo.exe
-  File "foo.ml", line 1, characters 14-19:
+  File "foo.ml", line 1, characters 14-17:
   1 | print_endline Bar.v;;
-                    ^^^^^
+                    ^^^
   Error: Unbound module Bar
   [1]
diff --git a/test/blackbox-tests/test-cases/instrumentation.t/ppx/hello_ppx.ml b/test/blackbox-tests/test-cases/instrumentation.t/ppx/hello_ppx.ml
index 28b5bf122b6..ffcd0b355a0 100644
--- a/test/blackbox-tests/test-cases/instrumentation.t/ppx/hello_ppx.ml
+++ b/test/blackbox-tests/test-cases/instrumentation.t/ppx/hello_ppx.ml
@@ -1,8 +1,6 @@
 open Ast_helper
-open Longident
 
 let place = ref None
-
 let file = ref None
 
 let read_file () =
@@ -10,32 +8,41 @@ let read_file () =
   | None -> "<none>"
   | Some s ->
     let ic = open_in s in
-    begin match input_line ic with
-    | exception End_of_file ->
-      close_in ic;
-      "<none>"
-    | s ->
-      close_in ic;
-      s
-    end
+    (match input_line ic with
+     | exception End_of_file ->
+       close_in ic;
+       "<none>"
+     | s ->
+       close_in ic;
+       s)
+;;
 
 let impl str =
   let arg =
     match !place with
-    | None -> Exp.ident (Location.mknoloc (Lident "__MODULE__"))
+    | None -> Exp.ident (Location.mknoloc (Longident.Lident "__MODULE__"))
     | Some s -> Exp.constant (Const.string (Printf.sprintf "%s (%s)" s (read_file ())))
   in
   Str.eval
-    (Exp.apply (Exp.ident (Location.mknoloc (Ldot (Lident "Hello", "hello"))))
-       [Nolabel, arg]) :: str
-
-open Ppxlib
+    (Exp.apply
+       (Exp.ident
+          (Location.mknoloc
+             (Longident.Ldot
+                ( { txt = Longident.Lident "Hello"; loc = Location.none }
+                , { txt = "hello"; loc = Location.none } ))))
+       [ Nolabel, arg ])
+  :: str
+;;
 
 let () =
-  Driver.add_arg "-place" (Arg.String (fun s -> place := Some s))
+  Ppxlib.Driver.add_arg
+    "-place"
+    (Arg.String (fun s -> place := Some s))
     ~doc:"PLACE where to say hello from";
-  Driver.add_arg "-file" (Arg.String (fun s -> file := Some s))
+  Ppxlib.Driver.add_arg
+    "-file"
+    (Arg.String (fun s -> file := Some s))
     ~doc:"Add info from file"
+;;
 
-let () =
-  Driver.register_transformation_using_ocaml_current_ast ~impl "hello"
+let () = Ppxlib.Driver.register_transformation_using_ocaml_current_ast ~impl "hello"
diff --git a/test/blackbox-tests/test-cases/melange/flags.t b/test/blackbox-tests/test-cases/melange/flags.t
index 2105904f479..1de650693e6 100644
--- a/test/blackbox-tests/test-cases/melange/flags.t
+++ b/test/blackbox-tests/test-cases/melange/flags.t
@@ -44,9 +44,9 @@ Trying to build triggers both warnings
   1 | let t = "\e\n" in
                ^^
   Error (warning 14 [illegal-backslash]): illegal backslash escape in string.
-  Hint: Single backslashes \ are reserved for escape sequences
-  (\n, \r, ...). Did you check the list of OCaml escape sequences?
-  To get a backslash character, escape it with a second backslash: \\.
+    Hint: Single backslashes \ are reserved for escape sequences (\n, \r, ...).
+    Did you check the list of OCaml escape sequences?
+    To get a backslash character, escape it with a second backslash: \\.
   File "main.ml", line 1, characters 4-5:
   1 | let t = "\e\n" in
           ^
@@ -83,9 +83,9 @@ Can also pass flags from the env stanza. Let's go back to failing state:
   1 | let t = "\e\n" in
                ^^
   Error (warning 14 [illegal-backslash]): illegal backslash escape in string.
-  Hint: Single backslashes \ are reserved for escape sequences
-  (\n, \r, ...). Did you check the list of OCaml escape sequences?
-  To get a backslash character, escape it with a second backslash: \\.
+    Hint: Single backslashes \ are reserved for escape sequences (\n, \r, ...).
+    Did you check the list of OCaml escape sequences?
+    To get a backslash character, escape it with a second backslash: \\.
   File "main.ml", line 1, characters 4-5:
   1 | let t = "\e\n" in
           ^
diff --git a/test/blackbox-tests/test-cases/melange/ppx-preview.t b/test/blackbox-tests/test-cases/melange/ppx-preview.t
index 5a7d7daa994..7ce6636b799 100644
--- a/test/blackbox-tests/test-cases/melange/ppx-preview.t
+++ b/test/blackbox-tests/test-cases/melange/ppx-preview.t
@@ -25,6 +25,8 @@ Show PPX snippet preview is shown in Dune
   $ export DUNE_SANDBOX=symlink
   $ dune build @melange
   File "lib/the_lib.ml", line 1, characters 7-11:
+  1 | let x: nope = "hello"
+             ^^^^
   Error: Unbound type constructor nope
   [1]
 
diff --git a/test/blackbox-tests/test-cases/melange/private-module.t/run.t b/test/blackbox-tests/test-cases/melange/private-module.t/run.t
index 3b010807809..ac82bec0b47 100644
--- a/test/blackbox-tests/test-cases/melange/private-module.t/run.t
+++ b/test/blackbox-tests/test-cases/melange/private-module.t/run.t
@@ -1,7 +1,7 @@
 X is not accessible as it is private
   $ dune build private-module/foo.js
-  File "foo.ml", line 1, characters 0-9:
+  File "foo.ml", line 1, characters 0-5:
   1 | Lib.X.run ();;
-      ^^^^^^^^^
+      ^^^^^
   Error: The module Lib.X is an alias for module Lib__X, which is missing
   [1]
diff --git a/test/blackbox-tests/test-cases/menhir/menhir-include-subdirs.t/run.t b/test/blackbox-tests/test-cases/menhir/menhir-include-subdirs.t/run.t
index 11b1ca90ef2..d4fd898eb77 100644
--- a/test/blackbox-tests/test-cases/menhir/menhir-include-subdirs.t/run.t
+++ b/test/blackbox-tests/test-cases/menhir/menhir-include-subdirs.t/run.t
@@ -10,10 +10,10 @@ Menhir in other places than the root of the file hierarchy.
   > }
 
   $ test unqualified
-  File "foo.ml", line 2, characters 2-14:
+  File "foo.ml", line 2, characters 2-5:
   2 |   Bar.Baz.unit (fun _ -> Bar.Baz.EOF) (Lexing.from_string "")
-        ^^^^^^^^^^^^
+        ^^^
   Error: Unbound module Bar
-  Hint: Did you mean Baz?
+  Hint:    Did you mean Baz?
   [1]
   $ test qualified
diff --git a/test/blackbox-tests/test-cases/meta-exports.t b/test/blackbox-tests/test-cases/meta-exports.t
index 40fe8f5e9d4..28e585f5da8 100644
--- a/test/blackbox-tests/test-cases/meta-exports.t
+++ b/test/blackbox-tests/test-cases/meta-exports.t
@@ -48,9 +48,9 @@ However, the compilation without `(implicit_transitive_deps)` fails:
   > EOF
 
   $ OCAMLPATH=$(pwd)/_install dune exec ./main.exe
-  File "main.ml", line 1, characters 19-24:
+  File "main.ml", line 1, characters 19-22:
   1 | let () = print_int Bar.x; print_newline ()
-                         ^^^^^
+                         ^^^
   Error: Unbound module Bar
   [1]
 
diff --git a/test/blackbox-tests/test-cases/ocamldep/ocamldep-error-check.t b/test/blackbox-tests/test-cases/ocamldep/ocamldep-error-check.t
index 3a0197af621..ecd63a4ef68 100644
--- a/test/blackbox-tests/test-cases/ocamldep/ocamldep-error-check.t
+++ b/test/blackbox-tests/test-cases/ocamldep/ocamldep-error-check.t
@@ -34,9 +34,9 @@ This check doesn't apply to single module libraries:
   > let x = Foo.x
   > EOF
   $ dune build @all
-  File "lib/foo.ml", line 1, characters 8-13:
+  File "lib/foo.ml", line 1, characters 8-11:
   1 | let x = Foo.x
-              ^^^^^
+              ^^^
   Error: Unbound module Foo
   [1]
   $ rm lib/foo.ml
@@ -64,9 +64,9 @@ Although we get slightly different behavior if wrapping is on or off:
   > (wrapped_executables false)
   > EOF
   $ dune exec ./exe/foo.exe
-  File "exe/foo.ml", line 1, characters 0-11:
+  File "exe/foo.ml", line 1, characters 0-3:
   1 | Foo.Bar.run ();;
-      ^^^^^^^^^^^
+      ^^^
   Error: Unbound module Foo
   [1]
 
diff --git a/test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-dev-tool-deps-conflict-project-deps.t b/test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-dev-tool-deps-conflict-project-deps.t
index 9415d29afd8..e0a6ff200e2 100644
--- a/test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-dev-tool-deps-conflict-project-deps.t
+++ b/test/blackbox-tests/test-cases/pkg/ocamlformat/ocamlformat-dev-tool-deps-conflict-project-deps.t
@@ -141,9 +141,9 @@ dev-tools don't leak into the project.
 
 There is no leak here. It is not taking Printer module from the printer of dev-tools dependency.
   $ dune exec -- foo
-  File "foo.ml", line 1, characters 9-22:
+  File "foo.ml", line 1, characters 9-16:
   1 | let () = Printer.print ()
-               ^^^^^^^^^^^^^
+               ^^^^^^^
   Error: Unbound module Printer
-  Hint: Did you mean Printexc or Printf?
+  Hint:    Did you mean Printexc or Printf?
   [1]
diff --git a/test/blackbox-tests/test-cases/private-modules/inaccessible-in-deps.t/run.t b/test/blackbox-tests/test-cases/private-modules/inaccessible-in-deps.t/run.t
index 28984e48abe..d1e5df5c63c 100644
--- a/test/blackbox-tests/test-cases/private-modules/inaccessible-in-deps.t/run.t
+++ b/test/blackbox-tests/test-cases/private-modules/inaccessible-in-deps.t/run.t
@@ -1,6 +1,6 @@
   $ dune build
-  File "foo.ml", line 1, characters 0-5:
+  File "foo.ml", line 1, characters 0-1:
   1 | X.run ();;
-      ^^^^^
+      ^
   Error: Unbound module X
   [1]
diff --git a/test/blackbox-tests/test-cases/private-modules/private-module-excluded-by-modules-field.t b/test/blackbox-tests/test-cases/private-modules/private-module-excluded-by-modules-field.t
index bf52c9b987c..8771490b108 100644
--- a/test/blackbox-tests/test-cases/private-modules/private-module-excluded-by-modules-field.t
+++ b/test/blackbox-tests/test-cases/private-modules/private-module-excluded-by-modules-field.t
@@ -31,9 +31,9 @@ X is warned about:
   Warning: These modules appear in the private_modules field:
   - X
   They must also appear in the modules field.
-  File "src/y.ml", line 1, characters 9-14:
+  File "src/y.ml", line 1, characters 9-10:
   1 | let () = X.foo ()
-               ^^^^^
+               ^
   Error: Unbound module X
   [1]
 
@@ -63,8 +63,8 @@ This warning should be ignored if we are in vendored_dirs
   $ cat > bar.ml
 
   $ dune build ./bar.exe
-  File "src/y.ml", line 1, characters 9-14:
+  File "src/y.ml", line 1, characters 9-10:
   1 | let () = X.foo ()
-               ^^^^^
+               ^
   Error: Unbound module X
   [1]
diff --git a/test/blackbox-tests/test-cases/private-package-lib/main.t b/test/blackbox-tests/test-cases/private-package-lib/main.t
index da4e081c8b2..5c5539f0309 100644
--- a/test/blackbox-tests/test-cases/private-package-lib/main.t
+++ b/test/blackbox-tests/test-cases/private-package-lib/main.t
@@ -137,9 +137,9 @@ But we shouldn't be able to access it directly:
   > print_endline Secret.secret
   > EOF
   $ dune exec ./subproj/subproj.exe
-  File "subproj/subproj.ml", line 1, characters 14-27:
+  File "subproj/subproj.ml", line 1, characters 14-20:
   1 | print_endline Secret.secret
-                    ^^^^^^^^^^^^^
+                    ^^^^^^
   Error: Unbound module Secret
   [1]
 
@@ -168,9 +168,9 @@ But we cannot use such libraries directly:
   > EOF
   $ dune exec --root use -- ./run.exe
   Entering directory 'use'
-  File "run.ml", line 1, characters 43-56:
+  File "run.ml", line 1, characters 43-49:
   1 | print_endline ("direct access attempt: " ^ Secret.secret)
-                                                 ^^^^^^^^^^^^^
+                                                 ^^^^^^
   Error: Unbound module Secret
   Leaving directory 'use'
   [1]
diff --git a/test/blackbox-tests/test-cases/transitive-deps-mode.t/run.t b/test/blackbox-tests/test-cases/transitive-deps-mode.t/run.t
index 5429f4a7c51..adc3e1ad0f0 100644
--- a/test/blackbox-tests/test-cases/transitive-deps-mode.t/run.t
+++ b/test/blackbox-tests/test-cases/transitive-deps-mode.t/run.t
@@ -1,6 +1,6 @@
 run should not access foo
   $ dune build ./run.exe 2>&1 | grep -v ocamlc
-  File "run.ml", line 1, characters 34-39:
+  File "run.ml", line 1, characters 34-37:
   1 | Printf.printf "Can't access %d\n" Foo.v
-                                        ^^^^^
+                                        ^^^
   Error: Unbound module Foo
diff --git a/test/blackbox-tests/test-cases/utop/utop-default/lib-in-root.t/run.t b/test/blackbox-tests/test-cases/utop/utop-default/lib-in-root.t/run.t
index 41ae25e7546..39f0fb069f0 100644
--- a/test/blackbox-tests/test-cases/utop/utop-default/lib-in-root.t/run.t
+++ b/test/blackbox-tests/test-cases/utop/utop-default/lib-in-root.t/run.t
@@ -1,7 +1,7 @@
 By default, dune utop tries to make a toplevel for the current directory:
 
   $ echo 'Stdlib.exit 0;;' | dune utop . -- -init "" | grep -v 'version'
-  Enter "#help;;" for help.
+  Enter #help;; for help.
   
   Init file not found: "".
   # 
diff --git a/test/blackbox-tests/test-cases/utop/utop-default/nothing-in-root.t/run.t b/test/blackbox-tests/test-cases/utop/utop-default/nothing-in-root.t/run.t
index 19ee048979c..58f470d6bc5 100644
--- a/test/blackbox-tests/test-cases/utop/utop-default/nothing-in-root.t/run.t
+++ b/test/blackbox-tests/test-cases/utop/utop-default/nothing-in-root.t/run.t
@@ -1,7 +1,7 @@
 Utop will load libs recursively:
 
   $ echo 'Stdlib.exit 0;;' | dune utop . -- -init "" | grep -v 'version'
-  Enter "#help;;" for help.
+  Enter #help;; for help.
   
   Init file not found: "".
   # 
diff --git a/test/blackbox-tests/test-cases/wrapped-transition.t/run.t b/test/blackbox-tests/test-cases/wrapped-transition.t/run.t
index 015b6b9271d..3765bee07f1 100644
--- a/test/blackbox-tests/test-cases/wrapped-transition.t/run.t
+++ b/test/blackbox-tests/test-cases/wrapped-transition.t/run.t
@@ -1,18 +1,18 @@
   $ dune build 2>&1 | grep -v ocamlc
-  File "fooexe.ml", line 3, characters 0-7:
+  File "fooexe.ml", line 3, characters 0-3:
   3 | Bar.run ();;
-      ^^^^^^^
+      ^^^
   Error (alert deprecated): module Bar
   Will be removed past 2020-20-20. Use Mylib.Bar instead.
   
-  File "fooexe.ml", line 4, characters 0-7:
+  File "fooexe.ml", line 4, characters 0-3:
   4 | Foo.run ();;
-      ^^^^^^^
+      ^^^
   Error (alert deprecated): module Foo
   Will be removed past 2020-20-20. Use Mylib.Foo instead.
   
-  File "fooexe.ml", line 7, characters 11-22:
+  File "fooexe.ml", line 7, characters 11-20:
   7 | module X : Intf_only.S = struct end
-                 ^^^^^^^^^^^
+                 ^^^^^^^^^
   Error (alert deprecated): module Intf_only
   Will be removed past 2020-20-20. Use Mylib.Intf_only instead.