diff --git a/Dockerfile b/Dockerfile
index c47493c..873acfd 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -56,7 +56,7 @@ RUN apt-get update \
     && docker-php-ext-enable $PHP_EXTENSIONS $PECL_PASSBOLT_EXTENSIONS \
     && docker-php-source delete \
     && EXPECTED_SIGNATURE=$(curl -s https://composer.github.io/installer.sig) \
-    && php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');" \
+    && curl -o composer-setup.php https://getcomposer.org/installer \
     && ACTUAL_SIGNATURE=$(php -r "echo hash_file('SHA384', 'composer-setup.php');") \
     && if [ "$EXPECTED_SIGNATURE" != "$ACTUAL_SIGNATURE" ]; then \
          >&2 echo 'ERROR: Invalid installer signature'; \