diff --git a/Dockerfile b/Dockerfile
index 63e511d..f7478f9 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -130,9 +130,9 @@ COPY src/replays/*        /app/danser/custom-replays/
 COPY src/settings/*       /app/danser/settings/
 COPY src/default-skin/    /app/danser/skins/default-skin/
 
-# non-root user 1000:1000
-RUN groupadd -g 1000 appuser && \
-    useradd -u 1000 -g 1000 -m -s /bin/bash appuser && \
+# non-root user 1000:1000 (safe even if uid/gid already exist)
+RUN groupadd -g 1000 appuser 2>/dev/null || true && \
+    id -u 1000 >/dev/null 2>&1 || useradd -u 1000 -g 1000 -m -s /bin/bash appuser && \
     chown -R 1000:1000 /app
 
 USER 1000:1000