diff --git a/tools/prepare_release.sh b/tools/prepare_release.sh
index 252569b..472aa21 100755
--- a/tools/prepare_release.sh
+++ b/tools/prepare_release.sh
@@ -2,9 +2,14 @@
 
 set -euo pipefail
 
-VERSION="$(jq -r '.version' ./package.json)"
+VERSION=${1-}
 REQUIRED_TOOLS="jq git"
 
+if test -z "$VERSION"; then
+  echo "Missing version parameter. Usage: $0 VERSION"
+  exit 1
+fi
+
 for tool in $REQUIRED_TOOLS; do
   if ! hash "$tool" 2>/dev/null; then
     echo "This script requires '$tool', but it is not installed."
@@ -17,6 +22,8 @@ if git rev-parse "v$VERSION" >/dev/null 2>&1; then
   exit 1
 fi
 
+jq --arg new_version "$VERSION" '.version = ($new_version)' package.json > tmp.json && mv tmp.json package.json
+
 git commit -a -m "prepare release v$VERSION"
 
 git tag -a "v$VERSION" -m "$VERSION"