@@ -17,8 +17,9 @@ ENV NODE_OPTIONS=--max-old-space-size=4096
 RUN npm install -g pnpm@11.5.2
 
 WORKDIR /app
-# git is needed to fetch the scratch-gui (and its scratch-blocks) GitHub deps.
-RUN apt-get update && apt-get install -y --no-install-recommends git && rm -rf /var/lib/apt/lists/*
+# git fetches the scratch-gui (and scratch-blocks) GitHub deps; a headless JRE is
+# needed because scratch-blocks' build runs the Java-based Google Closure Compiler.
+RUN apt-get update && apt-get install -y --no-install-recommends git default-jre-headless && rm -rf /var/lib/apt/lists/*
 
 # In the monorepo, allowBuilds lives in the root pnpm-workspace.yaml. The Docker
 # context is just this package, so we supply an equivalent settings file to permit