diff --git a/Dockerfile b/Dockerfile
index e12d33a..ee0edda 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -20,7 +20,10 @@ COPY 404.html /var/www/localhost/htdocs/404.html
 RUN mkdir /var/opt/out
 
 FROM alpine:3.23.4
-RUN apk update && apk upgrade && apk add --no-cache nodejs yarn nginx nginx-mod-http-headers-more && rm -rf /var/cache/apk/*
+# graphicsmagick is required at runtime too — the gm npm wrapper shells out to the
+# `gm`/`convert` binary on every upload; the builder stage has it, but the runtime
+# stage does not unless we add it here.
+RUN apk update && apk upgrade && apk add --no-cache nodejs yarn nginx nginx-mod-http-headers-more graphicsmagick && rm -rf /var/cache/apk/*
 
 COPY --from=builder /usr/share/vnc-avatar /usr/share/vnc-avatar
 COPY --from=builder /var/opt/out /var/opt/out