diff --git a/Dockerfile b/Dockerfile
index 4ec67df..6a9fefd 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -8,4 +8,8 @@ COPY run.sh /
 EXPOSE 514/tcp
 EXPOSE 514/udp
 
+ENV TARGET_HOST
+ENV TARGET_PROTO
+ENV TARGET_PORT
+
 ENTRYPOINT ["/bin/sh", "/run.sh"]
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