diff --git a/Dockerfile.standalone b/Dockerfile.standalone
index 6138f78..3077da3 100644
--- a/Dockerfile.standalone
+++ b/Dockerfile.standalone
@@ -8,10 +8,10 @@ COPY wokwi-libs/avr8js/ wokwi-libs/avr8js/
 WORKDIR /app/wokwi-libs/avr8js
 RUN npm install && npm run build --if-present
 
-# Build rp2040js (dist may already be committed; build only if script exists)
+# Build rp2040js (submodule may be empty on CI; skip if no package.json)
 COPY wokwi-libs/rp2040js/ wokwi-libs/rp2040js/
 WORKDIR /app/wokwi-libs/rp2040js
-RUN npm install && npm run build --if-present
+RUN if [ -f package.json ]; then npm install && npm run build --if-present; fi
 
 # Build wokwi-elements
 COPY wokwi-libs/wokwi-elements/ wokwi-libs/wokwi-elements/