diff --git a/cron/Dockerfile b/cron/Dockerfile
index edb6407fdb..c14304eb89 100644
--- a/cron/Dockerfile
+++ b/cron/Dockerfile
@@ -1,8 +1,8 @@
 ARG BASE_IMAGE
 FROM ${BASE_IMAGE}
 USER 0
-RUN if [ -z "${http_proxy}" ]; then echo "Acquire::http::proxy \"${http_proxy}\";" >> /etc/apt/apt.conf; fi
-RUN if [ -z "${https_proxy}" ]; then echo "Acquire::https::proxy \"${https_proxy}\";" >> /etc/apt/apt.conf; fi
+RUN if [ -n "${http_proxy}" ]; then echo "Acquire::http::proxy \"${http_proxy}\";" >> /etc/apt/apt.conf; fi
+RUN if [ -n "${https_proxy}" ]; then echo "Acquire::https::proxy \"${https_proxy}\";" >> /etc/apt/apt.conf; fi
 RUN apt-get update && apt-get install -y --no-install-recommends cron && \
     rm -r /var/lib/apt/lists/*
 COPY entrypoint.sh /entrypoint.sh