diff --git a/.scripts/mk-package.sh b/.scripts/mk-package.sh
index 401c2cdef17..1f9b7ec472b 100755
--- a/.scripts/mk-package.sh
+++ b/.scripts/mk-package.sh
@@ -1,34 +1,109 @@
 #!/bin/bash
 
+set -eu
+
 # This will just create a tar.gz or zip out of a directory.
 # You may want to look at src-install.sh and bin-install.sh
 # that generate the layouts for a source and binary package,
 # and are then packaged up with this script.
 
 if [ $# -ne 2 ]; then
-	echo "usage: $0 <install_root> <package_basename>" >&2
-	echo "Default format is tar.gz. Optionally set FSTAR_PACKAGE_FORMAT=zip to generate a zip instead." >&2
-	echo "Output filename is <package_basename> + proper extension." >&2
-	exit 1
+  exec >&2
+  echo "usage: $0 <install_root> <package_basename>"
+  echo "The archive format and command used depends on the system and installed tools,"
+  echo "see script for details."
+  echo "Optionally set FSTAR_PACKAGE_FORMAT to: "
+  echo " - 'zip': create a .zip via 'zip' command"
+  echo " - '7z': create a .zip via '7z' command"
+  echo " - 'tar.gz': create a .tar.gz, via calling"
+  echo "Output filename is <package_basename> + proper extension"
+  echo "If FSTAR_RELEASE is non-empty, we use maximum compression."
+  exit 1
 fi
 
 PREFIX="$1"
 ARCHIVE="$2"
 
+windows () {
+  [ -v OS ] && [ "$OS" = "Windows_NT" ]
+}
+
+# Computes a (hopefully) sensible default for the current system
+detect_format () {
+  if windows; then
+    # Github actions runner do not have 'zip'
+    if which zip > /dev/null; then
+      FSTAR_PACKAGE_FORMAT=zip
+    elif which 7z > /dev/null; then
+      FSTAR_PACKAGE_FORMAT=7z
+    else
+      echo "error: no zip or 7z command found." >&2
+      exit 1
+    fi
+  else
+    FSTAR_PACKAGE_FORMAT=tar.gz
+  fi
+}
+
+# If unset, pick a default for the system.
+if ! [ -v FSTAR_PACKAGE_FORMAT ]; then
+  detect_format
+fi
+
+# Fix for stupid path confustion in windows
+if windows; then
+  WRAP=$(pwd)/mk/winwrap.sh
+else
+  WRAP=
+fi
+
 case $FSTAR_PACKAGE_FORMAT in
   zip)
     TGT="$ARCHIVE.zip"
-    TGT="$(realpath "$TGT")"
-    pushd "$PREFIX"
-    zip -q -r -9 "$TGT" .
-    popd
+    ATGT="$(realpath "$TGT")"
+    pushd "$PREFIX" >/dev/null
+    LEVEL=
+    if [ -v FSTAR_RELEASE ]; then
+      LEVEL=-9
+    fi
+    $WRAP zip -q -r $LEVEL "$ATGT" .
+    popd >/dev/null
     ;;
-  tar.gz|tgz|"")
+  7z)
+    TGT="$ARCHIVE.zip"
+    ATGT="$(realpath "$TGT")"
+    LEVEL=
+    if [ -v FSTAR_RELEASE ]; then
+      LEVEL=-mx9
+    fi
+    pushd "$PREFIX" >/dev/null
+    $WRAP 7z $LEVEL a "$ATGT" .
+    popd >/dev/null
+    ;;
+  tar.gz|tgz)
     # -h: resolve symlinks
-    tar czf "$ARCHIVE.tar.gz" -h -C "$PREFIX" .
+    TGT="$ARCHIVE.tar.gz"
+    $WRAP tar cf "$ARCHIVE.tar" -h -C "$PREFIX" .
+    LEVEL=
+    if [ -v FSTAR_RELEASE ]; then
+      LEVEL=-9
+    fi
+    $WRAP gzip -f $LEVEL "$ARCHIVE.tar"
     ;;
   *)
     echo "unrecognized FSTAR_PACKAGE_FORMAT: $FSTAR_PACKAGE_FORMAT" >&2
     exit 1
     ;;
 esac
+
+if ! [ -f "$TGT" ] ; then
+  echo "error: something seems wrong, archive '$TGT' not found?" >&2
+  exit 1
+fi
+
+# bytes=$(stat -c%s "$TGT")
+# echo "Wrote $TGT" ($bytes bytes)"
+# ^ Does not work in Mac (no -c option for stat)
+
+echo "Wrote $TGT"
+ls -l "$TGT" || true