diff --git a/scripts/prepare_release.sh b/scripts/prepare_release.sh
index 3b63ed9e6c..229413e872 100755
--- a/scripts/prepare_release.sh
+++ b/scripts/prepare_release.sh
@@ -1,70 +1,39 @@
 #!/bin/bash
-
-print_usage()
-{
-    cat <<EOF
-Usage: $0 [OPTION]...
-Prepare the source tree for a release.
-
-Options:
-  -u    Prepare for development (undo the release preparation)
-EOF
-}
-
 # Copyright The Mbed TLS Contributors
 # SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 
+# prepare_release.sh — Prepare the source tree for a release.
+#
+# This script switches the repo into “release” mode:
+#   - Updates all tracked `.gitignore` files to stop
+#     ignoring the automatically-generated files.
+#   - Sets the CMake option `GEN_FILES` to OFF to explicitely disable
+#     recreating the automatically-generated files.
+#.  - The script will recursively update the tf-psa-crypto files too.
+
+
 set -eu
 
-if [ $# -ne 0 ] && [ "$1" = "--help" ]; then
-    print_usage
-    exit
-fi
-
-unrelease= # if non-empty, we're in undo-release mode
-while getopts u OPTLET; do
-    case $OPTLET in
-        u) unrelease=1;;
-        \?)
-            echo 1>&2 "$0: unknown option: -$OPTLET"
-            echo 1>&2 "Try '$0 --help' for more information."
-            exit 3;;
-    esac
-done
-
-
+# Portable inline sed. Helper function that will automatically pre-pend
+# an empty string as the backup suffix (required by macOS sed).
+psed() {
+    # macOS sed does not offer a version
+    if sed --version >/dev/null 2>&1; then
+        sed -i "$@"
+    # macOS/BSD sed
+    else
+        sed -i '' "$@"
+    fi
+}
 
 #### .gitignore processing ####
-
-GITIGNORES=$(find . -name ".gitignore")
-for GITIGNORE in $GITIGNORES; do
-    if [ -n "$unrelease" ]; then
-        sed -i '/###START_COMMENTED_GENERATED_FILES###/,/###END_COMMENTED_GENERATED_FILES###/s/^#//' $GITIGNORE
-        sed -i 's/###START_COMMENTED_GENERATED_FILES###/###START_GENERATED_FILES###/' $GITIGNORE
-        sed -i 's/###END_COMMENTED_GENERATED_FILES###/###END_GENERATED_FILES###/' $GITIGNORE
-    else
-        sed -i '/###START_GENERATED_FILES###/,/###END_GENERATED_FILES###/s/^/#/' $GITIGNORE
-        sed -i 's/###START_GENERATED_FILES###/###START_COMMENTED_GENERATED_FILES###/' $GITIGNORE
-        sed -i 's/###END_GENERATED_FILES###/###END_COMMENTED_GENERATED_FILES###/' $GITIGNORE
-    fi
+for GITIGNORE in $(git ls-files --recurse-submodules -- '*.gitignore'); do
+        psed '/###START_GENERATED_FILES###/,/###END_GENERATED_FILES###/s/^/#/' "$GITIGNORE"
+        psed 's/###START_GENERATED_FILES###/###START_COMMENTED_GENERATED_FILES###/' "$GITIGNORE"
+        psed 's/###END_GENERATED_FILES###/###END_COMMENTED_GENERATED_FILES###/' "$GITIGNORE"
 done
 
-
-
 #### Build scripts ####
+psed 's/^\(GEN_FILES[ ?:]*=\)\([^#]*\)/\1/' Makefile */Makefile
+psed '/[Oo][Ff][Ff] in development/! s/^\( *option *( *GEN_FILES  *"[^"]*"  *\)\([A-Za-z0-9][A-Za-z0-9]*\)/\1OFF/' CMakeLists.txt
 
-# GEN_FILES defaults on (non-empty) in development, off (empty) in releases
-if [ -n "$unrelease" ]; then
-    r=' yes'
-else
-    r=''
-fi
-sed -i 's/^\(GEN_FILES[ ?:]*=\)\([^#]*\)/\1'"$r/" Makefile */Makefile
-
-# GEN_FILES defaults on in development, off in releases
-if [ -n "$unrelease" ]; then
-    r='ON'
-else
-    r='OFF'
-fi
-sed -i '/[Oo][Ff][Ff] in development/! s/^\( *option *( *GEN_FILES  *"[^"]*"  *\)\([A-Za-z0-9][A-Za-z0-9]*\)/\1'"$r/" CMakeLists.txt