diff --git a/.github/scripts/main/ocaml-cache.sh b/.github/scripts/main/ocaml-cache.sh
index ac94f664775..d447aee3e8f 100644
--- a/.github/scripts/main/ocaml-cache.sh
+++ b/.github/scripts/main/ocaml-cache.sh
@@ -45,10 +45,12 @@ case "$HOST" in
 esac
 
 FLEXDLL_VERSION=0.43
+MINGW_W64_VERSION=12.0.0
 
 curl -sLO "https://github.com/ocaml/ocaml/archive/refs/tags/${OCAML_VERSION}.tar.gz"
 if [[ $PLATFORM = 'Windows' ]] ; then
   curl -sLO "https://github.com/ocaml/flexdll/archive/refs/tags/$FLEXDLL_VERSION.tar.gz"
+  curl -sLO "https://github.com/mingw-w64/mingw-w64/archive/refs/tags/v${MINGW_W64_VERSION}.tar.gz"
 fi
 
 tar -xzf "$OCAML_VERSION.tar.gz"
@@ -72,6 +74,11 @@ if [[ $PLATFORM = 'Windows' ]] ; then
   tar -xzf ../$FLEXDLL_VERSION.tar.gz
   rm -rf flexdll
   mv "flexdll-$FLEXDLL_VERSION" flexdll
+
+  tar -xzf "../v${MINGW_W64_VERSION}.tar.gz"
+  rm -rf winpthreads
+  mv "mingw-w64-${MINGW_W64_VERSION}/mingw-w64-libraries/winpthreads" winpthreads
+  rm -rf "mingw-w64-${MINGW_W64_VERSION}"
 fi
 
 if [[ $PLATFORM = 'macOS' ]]; then
@@ -115,7 +122,7 @@ if [[ $OPAM_TEST -ne 1 ]] ; then
   fi
 fi
 
-if ! ./configure --prefix "$PREFIX"$HOST --with-vendored-deps ${CONFIGURE_SWITCHES:-} ; then
+if ! ./configure --prefix "$PREFIX"$HOST ${CONFIGURE_SWITCHES:-} ; then
   echo
   echo -e "[\e[31mERROR\e[0m] OCaml's configure script failed"
   (set +x ; echo -en "::group::config.log contents\r") 2>/dev/null
diff --git a/.github/workflows/ci.ml b/.github/workflows/ci.ml
index 55627ae27a5..2077b8742c9 100644
--- a/.github/workflows/ci.ml
+++ b/.github/workflows/ci.ml
@@ -14,11 +14,11 @@
 open Lib
 
 let latest_ocaml4 = "4.14.2"
-let latest_ocaml5 = "5.2.0" (* Add this number to ocamls below when the next version comes out *)
+let latest_ocaml5 = "5.3.0" (* Add this number to ocamls below when the next version comes out *)
 let ocamls = [
   (* Fully supported versions *)
   "4.08.1"; "4.09.1"; "4.10.2"; "4.11.2"; "4.12.1"; "4.13.1";
-  "5.0.0"; "5.1.1";
+  "5.0.0"; "5.1.1"; "5.2.0";
 
   (* The last elements of the list after 4.14 will be used as default versions *)
   latest_ocaml4; latest_ocaml5;
@@ -312,8 +312,9 @@ let main_build_job ~analyse_job ~cygwin_job ?section runner start_version ~oc ~w
           "x86_64-pc-windows"
         ] in
         let ocaml5 = [
+          "x86_64-pc-cygwin";
           "x86_64-w64-mingw32";
-          (* "x86_64-pc-windows"; 5.3 needed *)
+          "x86_64-pc-windows";
         ] in
         let matrix_elem ocamlv hosts =
           let elem ocaml host =
@@ -526,7 +527,7 @@ let main oc : unit =
     (* These should be identical to the values in appveyor.yml *)
     ("OPAM_REPO", "https://github.com/ocaml/opam-repository.git");
     ("OPAM_TEST_REPO_SHA", "dff745994c64d083a6ba3ddc5a9c28ed0ad0f40a");
-    ("OPAM_REPO_SHA", "6eee105e52e098e36949a584c053a18bcb9b2f6b");
+    ("OPAM_REPO_SHA", "f93eb7cb02fb91bfd11535b3ce693d313341dd60");
     ("SOLVER", "");
     (* Cygwin configuration *)
     ("CYGWIN_MIRROR", "http://mirrors.kernel.org/sourceware/cygwin/");
diff --git a/.github/workflows/lib.ml b/.github/workflows/lib.ml
index d5f5864c7fa..28158722845 100644
--- a/.github/workflows/lib.ml
+++ b/.github/workflows/lib.ml
@@ -110,7 +110,7 @@ let find_need need = Hashtbl.find jobs need
 let emit_runs_on ~oc runs_on =
   let runner_of_platform (type a) (platform : a platform) =
     match platform with
-    | Windows -> "windows-2019"
+    | Windows -> "windows-2022"
     | MacOS
     | Linux as platform -> os_name_of_platform platform ^ "-latest"
     | Specific (platform, version) -> os_name_of_platform platform ^ "-" ^ version
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index d70e30df71c..dc6c192f0da 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -27,7 +27,7 @@ env:
   OPAM12CACHE: ~/.cache/opam1.2/cache
   OPAM_REPO: https://github.com/ocaml/opam-repository.git
   OPAM_TEST_REPO_SHA: dff745994c64d083a6ba3ddc5a9c28ed0ad0f40a
-  OPAM_REPO_SHA: 6eee105e52e098e36949a584c053a18bcb9b2f6b
+  OPAM_REPO_SHA: f93eb7cb02fb91bfd11535b3ce693d313341dd60
   SOLVER:
   CYGWIN_MIRROR: http://mirrors.kernel.org/sourceware/cygwin/
   CYGWIN_ROOT: D:\cygwin
@@ -79,7 +79,7 @@ jobs:
       run: bash -exu .github/scripts/main/archives-cache.sh
 
   Cygwin:
-    runs-on: windows-2019
+    runs-on: windows-2022
     needs: Analyse
     steps:
     - name: Cygwin64 Cache
@@ -106,7 +106,7 @@ jobs:
     needs: Analyse
     strategy:
       matrix:
-        ocamlv: [ 4.08.1, 4.09.1, 4.10.2, 4.11.2, 4.12.1, 4.13.1, 5.0.0, 5.1.1, 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.08.1, 4.09.1, 4.10.2, 4.11.2, 4.12.1, 4.13.1, 5.0.0, 5.1.1, 5.2.0, 4.14.2, 5.3.0 ]
       fail-fast: true
     steps:
     - name: Install bubblewrap
@@ -139,7 +139,7 @@ jobs:
       run: bash -exu .github/scripts/main/test.sh
 
   Build-Windows:
-    runs-on: windows-2019
+    runs-on: windows-2022
     needs: [ Analyse, Cygwin ]
     strategy:
       matrix:
@@ -159,9 +159,15 @@ jobs:
           - host: x86_64-pc-windows
             build: x86_64-pc-cygwin
             ocamlv: 4.14.2
+          - host: x86_64-pc-cygwin
+            build: x86_64-pc-cygwin
+            ocamlv: 5.3.0
           - host: x86_64-w64-mingw32
             build: x86_64-pc-cygwin
-            ocamlv: 5.2.0
+            ocamlv: 5.3.0
+          - host: x86_64-pc-windows
+            build: x86_64-pc-cygwin
+            ocamlv: 5.3.0
       fail-fast: false
     defaults:
       run:
@@ -244,7 +250,7 @@ jobs:
     needs: Analyse
     strategy:
       matrix:
-        ocamlv: [ 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.14.2, 5.3.0 ]
       fail-fast: true
     steps:
     - name: Install GNU patch
@@ -282,7 +288,7 @@ jobs:
     needs: [ Analyse, Build-Linux ]
     strategy:
       matrix:
-        ocamlv: [ 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.14.2, 5.3.0 ]
       fail-fast: false
     env:
       OPAM_TEST: 1
@@ -339,7 +345,7 @@ jobs:
     needs: Analyse
     strategy:
       matrix:
-        ocamlv: [ 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.14.2, 5.3.0 ]
       fail-fast: false
     env:
       OPAM_TEST: 1
@@ -428,7 +434,7 @@ jobs:
     needs: [ Analyse, Build-Linux ]
     strategy:
       matrix:
-        ocamlv: [ 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.14.2, 5.3.0 ]
       fail-fast: false
     env:
       OPAM_DOC: 1
@@ -485,7 +491,7 @@ jobs:
     strategy:
       matrix:
         solver: [ z3, 0install ]
-        ocamlv: [ 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.14.2, 5.3.0 ]
       fail-fast: false
     env:
       SOLVER: ${{ matrix.solver }}
@@ -535,7 +541,7 @@ jobs:
     strategy:
       matrix:
         solver: [ z3, 0install ]
-        ocamlv: [ 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.14.2, 5.3.0 ]
       fail-fast: false
     env:
       SOLVER: ${{ matrix.solver }}
@@ -583,7 +589,7 @@ jobs:
     needs: [ Analyse, Build-Linux ]
     strategy:
       matrix:
-        ocamlv: [ 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.14.2, 5.3.0 ]
       fail-fast: false
     steps:
     - name: Install bubblewrap
@@ -618,7 +624,7 @@ jobs:
     needs: [ Analyse, Build-macOS ]
     strategy:
       matrix:
-        ocamlv: [ 4.14.2, 5.2.0 ]
+        ocamlv: [ 4.14.2, 5.3.0 ]
       fail-fast: false
     steps:
     - name: Checkout tree
diff --git a/master_changes.md b/master_changes.md
index 45b56deb343..4cf964683c7 100644
--- a/master_changes.md
+++ b/master_changes.md
@@ -162,6 +162,8 @@ users)
   * Update the github action scripts now that homebrew renamed the GNU patch binary to gpatch [#6296 @kit-ty-kate]
   * Add branch scheme `username/branch` for opam-rt specific branch to use [#6274 @rjbou]
   * Check `shell/install.sh` using `shellcheck` [#6313 @kit-ty-kate]
+  * Add OCaml 5.3 to the build matrix [#6192 @kit-ty-kate]
+  * Add OCaml 5.3/Cygwin and OCaml 5.3/MSVC to the build matrix [#6192 @kit-ty-kate]
 
 ## Doc
   * Update the command to install opam to point to the new simplified url on opam.ocaml.org [#6226 @kit-ty-kate]