diff --git a/dockerfile b/dockerfile
index c72b44d..89e1599 100644
--- a/dockerfile
+++ b/dockerfile
@@ -13,7 +13,9 @@ ENV DATABASE_URL=postgresql://user:pass@localhost:5432/papo?schema=public
 ENV PRISMA_IGNORE_ENV_LOAD=true
 
 # Install dependencies (inkl. dev)
-COPY package*.json ./
+COPY package.json package-lock.json ./
+# fail fast if lockfile missing in build context
+RUN test -f package-lock.json
 RUN npm ci --include=dev
 
 # Ensure prisma CLI available globally (avoids path issues)