diff --git a/Dockerfile b/Dockerfile
index 1537258..ad5120a 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -31,8 +31,8 @@ RUN mkdir -p /usr/share/webapps/cops
 RUN wget -qO- https://github.com/seblucas/cops/archive/$VERSION.tar.gz | tar xz -C /usr/share/webapps/cops --strip 1
 
 WORKDIR /usr/share/webapps/cops
-RUN wget https://getcomposer.org/composer.phar
-RUN php composer.phar global require "fxp/composer-asset-plugin:~1.1"
+RUN wget https://getcomposer.org/download/1.9.0/composer.phar
+RUN php composer.phar --no-plugins global require "fxp/composer-asset-plugin:~1.1"
 RUN php composer.phar install --no-dev --optimize-autoloader
 
 RUN chown -R nginx:nginx /usr/share/webapps/cops