diff --git a/doc/pages/Manual.md b/doc/pages/Manual.md
index 062aaecf749..9b32efc36df 100644
--- a/doc/pages/Manual.md
+++ b/doc/pages/Manual.md
@@ -1125,6 +1125,9 @@ files.
     - `OPAMCLI=2.0` (since opam 2.1)
     - `TMP` and `TMPDIR` are set by the sandbox script (bubblewrap), but should not be relied on since the sandbox is not used on all platforms and can be disabled by the user.
 
+  See [`x-allow-env-path-rewrite-on-windows:`](#opamfield-x-allow-env-path-rewrite-on-windows)
+  for path portaility of environment variables on Windows.
+
 - <a id="opamsection-extra-sources">`extra-source <string> "{" <url-file> "}"`</a>:
   allows the definition of extra files that need downloading into the source
   tree before the package can be patched (if necessary) and built. The format is
@@ -1133,6 +1136,9 @@ files.
   `<string>` indicates the name the file should be saved to, and is relative to
   the root of the source tree.
 
+  See [`x-allow-env-path-rewrite-on-windows:`](#opamfield-x-allow-env-path-rewrite-on-windows)
+  for path portaility of environment variables on Windows.
+
 - <a id="opamfield-extra-files">`extra-files: [ [ <string> <checksum> ] ... ]`</a>:
   optionally lists the files below `files/` with their checksums. Used
   internally for integrity verifications.
@@ -1157,6 +1163,12 @@ files.
   extra fields prefixed with `x-` can be defined for use by external tools. opam
   will ignore them except for some search operations.
 
+- <a id="opamfield-x-allow-env-path-rewrite-on-windows">`x-allow-env-path-rewrite-on-windows: <bool>`</a>:
+  a specific extra field, used to specify if environment variables defined in
+  [`setenv:`](#opamfield-setenv) and [`build-env`](#opamfield-build-env) need a
+  rewriting for path separators on Windows. The default is false. For the
+  moment we use an extra field to not update opam file syntax.
+
 #### descr
 
 Descr is a plain UTF-8 text file without specific syntactic constraints. The
diff --git a/master_changes.md b/master_changes.md
index 28dcb5f0355..331d7037375 100644
--- a/master_changes.md
+++ b/master_changes.md
@@ -118,6 +118,7 @@ users)
   * Add coreutils install for cheksum validation tests [#5560 @rjbou]
 
 ## Doc
+  * Add an `x-allow-env-path-rewrite-on-windows:` field entry [#5636 @rjbou]
 
 ## Security fixes