diff --git a/.github/scripts/main/ocaml-cache.sh b/.github/scripts/main/ocaml-cache.sh
index c2e9f5e76ea..c9f578dc2cc 100644
--- a/.github/scripts/main/ocaml-cache.sh
+++ b/.github/scripts/main/ocaml-cache.sh
@@ -46,12 +46,12 @@ esac
 
 FLEXDLL_VERSION=0.43
 
-curl -sLO "https://caml.inria.fr/pub/distrib/ocaml-${OCAML_VERSION%.*}/ocaml-$OCAML_VERSION.tar.gz"
+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"
 fi
 
-tar -xzf "ocaml-$OCAML_VERSION.tar.gz"
+tar -xzf "$OCAML_VERSION.tar.gz"
 
 case "${OCAML_VERSION%.*}" in
   4.08) PATCHES='e322556b0a9097a2eff2117476193b773e1b947f 17df117b4939486d3285031900587afce5262c8c';;
diff --git a/master_changes.md b/master_changes.md
index dd13c9eef9c..04d32340323 100644
--- a/master_changes.md
+++ b/master_changes.md
@@ -72,11 +72,12 @@ users)
 
 ## Build
   * Fix the lower-bound constraint on ocaml-re (bump from >= 1.9.0 to >= 1.10.0) [#6016 @kit-ty-kate]
-  * Update source file location as caml.inria.fr is unavailable [#6032 @mtelvers]
+  * Update source file location as caml.inria.fr is unavailable [#6032 #5789 @mtelvers @kit-ty-kate]
 
 ## Infrastructure
 
 ## Release scripts
+  * Add windows to the release script [#5789 @kit-ty-kate]
 
 ## Install script
 
diff --git a/release/Makefile b/release/Makefile
index d559c8eb576..e55d57e48d5 100644
--- a/release/Makefile
+++ b/release/Makefile
@@ -4,10 +4,12 @@ OPAM_VERSION = $(subst -,~,$(VERSION))
 GIT_URL = ..
 
 OCAMLV = 4.14.2
+FLEXDLLV = 0.43
 # currently hardcoded in Dockerfile.in
-OCAML_URL = https://caml.inria.fr/pub/distrib/ocaml-$(basename $(OCAMLV))/ocaml-$(OCAMLV).tar.gz
+OCAML_URL = https://github.com/ocaml/ocaml/archive/refs/tags/$(OCAMLV).tar.gz
+FLEXDLL_URL = https://github.com/ocaml/flexdll/archive/refs/tags/$(FLEXDLLV).tar.gz
 
-HOST_OS = $(shell uname -s | tr A-Z a-z | sed 's/darwin/macos/')
+HOST_OS = $(shell uname -s | tr A-Z a-z | sed -e 's/_.*//' -e 's/darwin/macos/' -e 's/cygwin/windows/')
 HOST = $(shell uname -m | sed 's/amd64/x86_64/')-$(HOST_OS)
 OUTDIR = out/$(TAG)
 
@@ -70,6 +72,13 @@ CLINKING_macos = \
 CLINKING_openbsd = $(CLINKING_macos)
 CLINKING_freebsd = $(CLINKING_macos)
 
+CLINKING_windows = \
+-lunix -lmccs_stubs -lmccs_glpk_stubs $(SHA_LINK) \
+-lopam_stubs_win32_stubs \
+-l:libstdc++.a -l:libpthread.a \
+-Wl,-static \
+-ladvapi32 -lgdi32 -luser32 -lshell32 -lole32 -luuid -luserenv
+
 LINKING = (-noautolink $(patsubst %,-cclib %,$(CLINKING_$(1))))
 
 EXPORTS_openbsd = \
@@ -80,6 +89,7 @@ EXPORTS_freebsd = \
 CPATH=/usr/local/include: \
 LIBRARY_PATH=/usr/local/lib: \
 
+EXTRA_CONFIGURE_ARGS_windows = --host=x86_64-w64-mingw32 --with-flexdll
 
 %: opam-$(VERSION)-%
 
@@ -92,12 +102,18 @@ opam-$(VERSION)-%: $(OUTDIR)/opam-$(VERSION)-%
 build/$(HOST).env:
 	mkdir -p build/$(HOST)
 	cd build/$(HOST) && curl -OL $(OCAML_URL)
-	cd build/$(HOST) && tar xzf ocaml-$(OCAMLV).tar.gz
+	cd build/$(HOST) && tar xzf $(OCAMLV).tar.gz
+	cd build/$(HOST)/ocaml-$(OCAMLV) && curl -OL $(FLEXDLL_URL)
+	cd build/$(HOST)/ocaml-$(OCAMLV) && tar xzf $(shell basename "$(FLEXDLL_URL)")
+	cd build/$(HOST)/ocaml-$(OCAMLV) && rmdir flexdll && mv "flexdll-$(FLEXDLLV)" flexdll
 	cd build/$(HOST)/ocaml-$(OCAMLV) && \
-	  ./configure --prefix "$(shell pwd)/build/$(HOST)" && \
+	  ./configure --prefix "$(shell pwd)/build/$(HOST)" \
+	    --disable-debug-runtime --disable-debugger --disable-instrumented-runtime \
+	    --disable-ocamldoc --disable-stdlib-manpages --disable-ocamltest \
+	    $(EXTRA_CONFIGURE_ARGS_$(HOST_OS)) && \
 	  $(MAKE) -j$(JOBS) && \
 	  $(MAKE) install
-	rm -rf build/$(HOST)/ocaml-$(OCAMLV) build/$(HOST)/ocaml-$(OCAMLV).tar.gz
+	rm -rf build/$(HOST)/ocaml-$(OCAMLV) build/$(HOST)/$(OCAMLV).tar.gz
 	touch $@
 
 # Actually builds $(OUTDIR)/opam-$(VERSION)-$(HOST), but we don't want to override the
@@ -137,21 +153,24 @@ distclean: clean
 
 REMOTE_DIR = /tmp/opam-release
 REMOTE_MAKE = make
+REMOTE_SHELL = /bin/sh
 SSH = ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no
 SCP = scp -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no
 remote: $(OUTDIR)/opam-full-$(VERSION).tar.gz
-	$(SSH) "$(REMOTE)" "mkdir -p $(REMOTE_DIR)/${OUTDIR}"
+	$(SSH) "$(REMOTE)" "mkdir -p $(REMOTE_DIR)/$(OUTDIR)"
 	$(SCP) Makefile "$(REMOTE):$(REMOTE_DIR)/"
 	$(SCP) "$^" "$(REMOTE):$(REMOTE_DIR)/$^"
 	$(SSH) "$(REMOTE)" 'sh -c "cd $(REMOTE_DIR) && ulimit -s 8192 && $(REMOTE_MAKE) host TAG=$(TAG) VERSION=$(VERSION) OCAMLV=$(OCAMLV)"'
 	$(SCP) "$(REMOTE):$(REMOTE_DIR)/$(OUTDIR)/opam-$(VERSION)*" "$(OUTDIR)/"
 
+SSH_USER = root
+ULIMIT = ulimit -s 8192 &&
 qemu: $(OUTDIR)/opam-full-$(VERSION).tar.gz
-	$(SSH) -p "$(QEMU_PORT)" root@localhost "mkdir -p $(REMOTE_DIR)/${OUTDIR}"
-	$(SCP) -P "$(QEMU_PORT)" Makefile "root@localhost:$(REMOTE_DIR)/"
-	$(SCP) -P "$(QEMU_PORT)" "$^" "root@localhost:$(REMOTE_DIR)/$^"
-	$(SSH) -p "$(QEMU_PORT)" root@localhost 'sh -c "cd $(REMOTE_DIR) && ulimit -s 8192 && $(REMOTE_MAKE) host JOBS=$(JOBS) TAG=$(TAG) VERSION=$(VERSION) OCAMLV=$(OCAMLV)"'
-	$(SCP) -P "$(QEMU_PORT)" "root@localhost:$(REMOTE_DIR)/$(OUTDIR)/opam-$(VERSION)*" "$(OUTDIR)/"
+	$(SSH) -p "$(QEMU_PORT)" $(SSH_USER)@localhost "$(REMOTE_SHELL) -c \"mkdir -p $(REMOTE_DIR)/$(OUTDIR)\""
+	$(SCP) -P "$(QEMU_PORT)" Makefile "$(SSH_USER)@localhost:$(REMOTE_DIR)/"
+	$(SCP) -P "$(QEMU_PORT)" "$^" "$(SSH_USER)@localhost:$(REMOTE_DIR)/$^"
+	$(SSH) -p "$(QEMU_PORT)" $(SSH_USER)@localhost "$(REMOTE_SHELL) -c \"cd $(REMOTE_DIR) && $(ULIMIT) $(REMOTE_MAKE) host JOBS=$(JOBS) TAG=$(TAG) VERSION=$(VERSION) OCAMLV=$(OCAMLV)\""
+	$(SCP) -P "$(QEMU_PORT)" "$(SSH_USER)@localhost:$(REMOTE_DIR)/$(OUTDIR)/opam-$(VERSION)*" "$(OUTDIR)/"
 
 macos-local: $(OUTDIR)/opam-full-$(VERSION).tar.gz
 	LOCAL_RELEASE_DIR=$(shell mktemp -d); \
diff --git a/release/readme.md b/release/readme.md
index 8786f7be2e5..942da1baf76 100644
--- a/release/readme.md
+++ b/release/readme.md
@@ -7,6 +7,48 @@
 * run `make tests`, `opam-rt` [checked by github actions]
 * update the CHANGE file: take `master_changes.md` content to fill it
 
+## Windows setup
+
+* From the "release" directory (where this here readme.md file should be)...
+* Download Windows 10 English International 64bit from https://www.microsoft.com/en-gb/software-download/windows10ISO
+* Run qemu-img create -f qcow2 Windows-10-x86_64.qcow2 32G
+* Run qemu-system-x86_64 -cdrom Win10_22H2_EnglishInternational_x64v1.iso -drive file=Windows-10-x86_64.qcow2 -smp 8 -m 6G -net nic -net user,restrict=on -machine q35
+* Install Windows. Everything stays as default except:
+  * Click "I don’t have a product key"
+  * Choose "Windows 10 Pro"
+  * Click "Custom: ..." not "Upgrade: ..."
+* This will take an hour or so
+* Select the default keyboard then wait some more
+* Upon restart:
+  * no online account
+  * yes, i want the limited experience
+  * username: opam
+  * no password
+  * no location
+  * no find my device
+  * send required diagnostic data
+  * no improve inking & typing
+  * no cortana
+* Open gpedit.msc and right-click on "Computer Configuration -> Administrative Templates -> Windows Components -> Windows Update -> Configure Automatic Updates", click Edit and in the new window click on Enabled and then select "2. Notify for download and auto install", click Apply and then Ok.
+* Start -> Power off
+* Run qemu-system-x86_64 -drive file=Windows-10-x86_64.qcow2 -smp 8 -m 6G -machine q35
+* Answer yes to the "would you like to be discoverable on the network" prompt
+* Open the Settings app
+  * "System -> Power & Sleep" and select "Never" on the "When plugged in, turn off after" drop-down menu
+  * search for "Add an optional feature", then search for "OpenSSH" and install "OpenSSH Server"
+* Run services.msc
+  * Double-click OpenSSH SSH Server then select Automatic from the Startup drop-down menu
+  * Click Ok
+* Open cmd.exe as administrator and run "net start sshd", then "notepad C:/ProgramData/ssh/sshd_config"
+  * Uncomment and set:
+    * PermitEmptyPasswords yes
+    * PermitRootLogin yes
+    * PasswordAuthentication yes
+    * StrictMode no
+  * Save and close both applications
+* Open regedit.exe and set HKey_Local_Machine\SYSTEM\CurrentControlSet\Control\Lsa\LimitBlankPasswordUse to 0
+* Shutdown the computer using the startmenu button
+
 ## Github release
 
 [ once bump version & changes PRs merged ]
@@ -48,6 +90,7 @@
 
 ## Device requirements
 * Mac M1 or above with Rosetta2
+* >=70GB of disk space free
 * brew dependencies: git, gpg, qemu>=8.1.0, docker>=24.0.0, md5sha1sum (only when releasing on the 2.1 branch)
 * opam repo with the tag fetched
 * Have the secret key available
diff --git a/release/release.sh b/release/release.sh
index 70da16a0119..a74fb148332 100755
--- a/release/release.sh
+++ b/release/release.sh
@@ -32,6 +32,36 @@ SSH="ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no"
 OUTDIR="out/$TAG"
 mkdir -p "$OUTDIR"
 
+windows_build() {
+  local port=$1
+  local image=$2
+
+  if ! ${SSH} -p "${port}" opam@localhost cd; then
+    qemu-img convert -O raw "./${image}.qcow2" "./${image}.raw"
+    # NOTE: -machine q35 seems to be required to avoid random but recurring crashes
+    "qemu-system-x86_64" -drive "file=./${image}.raw,format=raw" -nic "user,hostfwd=tcp::${port}-:22" -m 6G -smp "${JOBS}" -machine q35 &
+    sleep 120
+  fi
+
+  # Disable Windows Defender before anything else (makes the build process faster)
+  # TODO: ... doesn't work
+  #       as well as the following line to add to the readme.md: Open the Windows Security app and turn off "Tamper Protection" and Real-time protection" from "Virus & threat protection -> Virus & threat protection settings -> Manage settings"
+  #${SSH} -p "${port}" opam@localhost "powershell -c 'Set-MpPreference -Force \
+  #                                    -DisableBehaviorMonitoring \$True \
+  #                                    -DisableRealtimeMonitoring \$True \
+  #                                    -DisableScriptScanning \$True \
+  #                                    -EnableLowCpuPriority \$True'"
+
+  ${SSH} -p "${port}" opam@localhost "curl -LO https://cygwin.com/setup-x86_64.exe"
+  ${SSH} -p "${port}" opam@localhost '.\setup-x86_64.exe -q -O -s https://cygwin.mirror.uk.sargasso.net -P make,diffutils,mingw64-x86_64-gcc-g++,mingw64-i686-gcc-g++,rsync,patch,curl,unzip,git,binutils'
+
+  make TAG="$TAG" JOBS="${JOBS}" qemu QEMU_PORT="${port}" REMOTE_MAKE=make REMOTE_DIR="opam-release-$TAG" 'REMOTE_SHELL=C:\Cygwin64\bin\bash.exe -l' SSH_USER=opam ULIMIT=""
+
+  ${SSH} -p "${port}" opam@localhost "shutdown /s /f"
+
+  wait
+}
+
 qemu_build() {
   local port=$1
   local image=$2
@@ -59,6 +89,6 @@ make JOBS="${JOBS}" TAG="$TAG" s390x-linux
 [ -f "${OUTDIR}/opam-$TAG-x86_64-macos" ] || make TAG="$TAG" JOBS="${JOBS}" macos-local MACOS_ARCH=x86_64 REMOTE_DIR=opam-release-$TAG GIT_URL="$CWD/.."
 [ -f "${OUTDIR}/opam-$TAG-arm64-macos" ] || make TAG="$TAG" JOBS="${JOBS}" macos-local MACOS_ARCH=arm64 REMOTE_DIR=opam-release-$TAG GIT_URL="$CWD/.."
 [ -d ./qemu-base-images ] || git clone https://gitlab.com/kit-ty-kate/qemu-base-images.git
-[ -f "${OUTDIR}/opam-$TAG-x86_64-openbsd" ] || qemu_build 9999 OpenBSD-7.4-amd64 "pkg_add gmake curl bzip2" gmake x86_64 &
-[ -f "${OUTDIR}/opam-$TAG-x86_64-freebsd" ] || qemu_build 9998 FreeBSD-13.2-RELEASE-amd64 "pkg install -y gmake curl bzip2" gmake x86_64 &
-wait
+[ -f "${OUTDIR}/opam-$TAG-x86_64-openbsd" ] || qemu_build 9999 OpenBSD-7.4-amd64 "pkg_add gmake curl bzip2" gmake x86_64
+[ -f "${OUTDIR}/opam-$TAG-x86_64-freebsd" ] || qemu_build 9998 FreeBSD-13.2-RELEASE-amd64 "pkg install -y gmake curl bzip2" gmake x86_64
+[ -f "${OUTDIR}/opam-$TAG-x86_64-windows" ] || windows_build 9997 Windows-10-x86_64
diff --git a/src_ext/Makefile b/src_ext/Makefile
index 419a8d6ee60..f652c0352c3 100644
--- a/src_ext/Makefile
+++ b/src_ext/Makefile
@@ -8,7 +8,7 @@ endif
 
 PATCH ?= patch
 
-URL_ocaml = https://github.com/ocaml/ocaml/archive/4.14.2.tar.gz
+URL_ocaml = https://github.com/ocaml/ocaml/archive/refs/tags/4.14.2.tar.gz
 MD5_ocaml = b28daefda803b5d5910cecf085b1451c
 
 URL_flexdll = https://github.com/ocaml/flexdll/archive/0.43.tar.gz