diff --git a/Containers/imaginary/Dockerfile b/Containers/imaginary/Dockerfile
index c3980fc4..caa473d5 100644
--- a/Containers/imaginary/Dockerfile
+++ b/Containers/imaginary/Dockerfile
@@ -31,5 +31,5 @@ USER nobody
 ENV MALLOC_ARENA_MAX=2
 ENTRYPOINT ["imaginary", "-return-size", "-max-allowed-resolution", "222.2"]
 
-HEALTHCHECK CMD nc -z localhost $PORT || exit 1
+HEALTHCHECK CMD nc -z localhost "$PORT" || exit 1
 LABEL com.centurylinklabs.watchtower.monitor-only="true"