diff --git a/Dockerfile b/Dockerfile
index ccd2346..6bdf7f8 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,18 +1,17 @@
- FROM debian:buster-slim
+FROM ubuntu:latest as smartdns-builder
 
- RUN apt update && \
-     apt install -y git make gcc libssl-dev && \
-     git clone https://github.com/pymumu/smartdns.git --depth 1 && \
+COPY . /smartdns/
+RUN  apt update && \
+     apt install -y make gcc libssl-dev && \
      cd smartdns && \
-     sh ./package/build-pkg.sh --platform debian --arch `dpkg --print-architecture` && \
-     dpkg -i package/*.deb && \
-     cd / && \
-     rm -rf smartdns/ && \
-     apt autoremove -y git make gcc libssl-dev && \
-     apt clean && \
-     rm -rf /var/lib/apt/lists/*
+     sh ./package/build-pkg.sh --platform debian --arch `dpkg --print-architecture`
 
- EXPOSE 53/udp
- VOLUME "/etc/smartdns/"
+FROM ubuntu:latest
+COPY --from=smartdns-builder /smartdns/package/*.deb /opt/
+RUN dpkg -i /opt/*.deb && \
+    rm /opt/*deb -fr
 
- CMD ["/usr/sbin/smartdns", "-f"]
+EXPOSE 53/udp
+VOLUME "/etc/smartdns/"
+
+CMD ["/usr/sbin/smartdns", "-f", "-x"]
diff --git a/src/dns_conf.c b/src/dns_conf.c
index 513b8d2..f715da5 100644
--- a/src/dns_conf.c
+++ b/src/dns_conf.c
@@ -1458,7 +1458,7 @@ static struct dns_ptr *_dns_conf_get_ptr(const char *ptr_domain)
 	key = hash_string(ptr_domain);
 	hash_for_each_possible(dns_ptr_table.ptr, ptr, node, key)
 	{
-		if (strncmp(ptr->ptr_domain, ptr_domain, DNS_MAX_CNAME_LEN) != 0) {
+		if (strncmp(ptr->ptr_domain, ptr_domain, DNS_MAX_PTR_LEN) != 0) {
 			continue;
 		}