diff --git a/docker/nginx/conf.d.templates/server.account.conf b/docker/nginx/conf.d.templates/server.account.conf
index 40f60f9b..c83cc208 100644
--- a/docker/nginx/conf.d.templates/server.account.conf
+++ b/docker/nginx/conf.d.templates/server.account.conf
@@ -10,7 +10,13 @@
 		server_name account.{{PORTAL_DOMAIN}}; # example: account.siasky.net
 
 		set_by_lua_block $skynet_portal_domain { return "{{PORTAL_DOMAIN}}" }
-		set_by_lua_block $skynet_server_domain { return "{{SERVER_DOMAIN}}" == "" and "{{PORTAL_DOMAIN}}" or "{{SERVER_DOMAIN}}" }
+		set_by_lua_block $skynet_server_domain {
+			-- fall back to portal domain if server domain is not defined
+			if "{{SERVER_DOMAIN}}" == "" then
+				return "{{PORTAL_DOMAIN}}"
+			end
+			return "{{SERVER_DOMAIN}}"
+		}
 
 		ssl_certificate     /data/caddy/caddy/certificates/acme-v02.api.letsencrypt.org-directory/wildcard_.{{PORTAL_DOMAIN}}/wildcard_.{{PORTAL_DOMAIN}}.crt;
 		ssl_certificate_key	/data/caddy/caddy/certificates/acme-v02.api.letsencrypt.org-directory/wildcard_.{{PORTAL_DOMAIN}}/wildcard_.{{PORTAL_DOMAIN}}.key;
diff --git a/docker/nginx/conf.d.templates/server.api.conf b/docker/nginx/conf.d.templates/server.api.conf
index 84c6b28d..0421ed29 100644
--- a/docker/nginx/conf.d.templates/server.api.conf
+++ b/docker/nginx/conf.d.templates/server.api.conf
@@ -9,7 +9,13 @@ server {
 	server_name {{PORTAL_DOMAIN}}; # example: siasky.net
 
 	set_by_lua_block $skynet_portal_domain { return "{{PORTAL_DOMAIN}}" }
-	set_by_lua_block $skynet_server_domain { return "{{SERVER_DOMAIN}}" == "" and "{{PORTAL_DOMAIN}}" or "{{SERVER_DOMAIN}}" }
+	set_by_lua_block $skynet_server_domain {
+		-- fall back to portal domain if server domain is not defined
+		if "{{SERVER_DOMAIN}}" == "" then
+			return "{{PORTAL_DOMAIN}}"
+		end
+		return "{{SERVER_DOMAIN}}"
+	}
 
 	ssl_certificate     /data/caddy/caddy/certificates/acme-v02.api.letsencrypt.org-directory/{{PORTAL_DOMAIN}}/{{PORTAL_DOMAIN}}.crt;
 	ssl_certificate_key	/data/caddy/caddy/certificates/acme-v02.api.letsencrypt.org-directory/{{PORTAL_DOMAIN}}/{{PORTAL_DOMAIN}}.key;
diff --git a/docker/nginx/conf.d.templates/server.hns.conf b/docker/nginx/conf.d.templates/server.hns.conf
index 94ce1aa8..bbd24d60 100644
--- a/docker/nginx/conf.d.templates/server.hns.conf
+++ b/docker/nginx/conf.d.templates/server.hns.conf
@@ -9,7 +9,13 @@ server {
 	server_name *.hns.{{PORTAL_DOMAIN}}; # example: *.hns.siasky.net
 	
 	set_by_lua_block $skynet_portal_domain { return "{{PORTAL_DOMAIN}}" }
-	set_by_lua_block $skynet_server_domain { return "{{SERVER_DOMAIN}}" == "" and "{{PORTAL_DOMAIN}}" or "{{SERVER_DOMAIN}}" }
+	set_by_lua_block $skynet_server_domain {
+		-- fall back to portal domain if server domain is not defined
+		if "{{SERVER_DOMAIN}}" == "" then
+			return "{{PORTAL_DOMAIN}}"
+		end
+		return "{{SERVER_DOMAIN}}"
+	}
 
 	ssl_certificate     /data/caddy/caddy/certificates/acme-v02.api.letsencrypt.org-directory/wildcard_.hns.{{PORTAL_DOMAIN}}/wildcard_.hns.{{PORTAL_DOMAIN}}.crt;
 	ssl_certificate_key	/data/caddy/caddy/certificates/acme-v02.api.letsencrypt.org-directory/wildcard_.hns.{{PORTAL_DOMAIN}}/wildcard_.hns.{{PORTAL_DOMAIN}}.key;
diff --git a/docker/nginx/conf.d.templates/server.skylink.conf b/docker/nginx/conf.d.templates/server.skylink.conf
index 0a70044c..792ad901 100644
--- a/docker/nginx/conf.d.templates/server.skylink.conf
+++ b/docker/nginx/conf.d.templates/server.skylink.conf
@@ -9,7 +9,13 @@ server {
 	server_name *.{{PORTAL_DOMAIN}}; # example: *.siasky.net
 	
 	set_by_lua_block $skynet_portal_domain { return "{{PORTAL_DOMAIN}}" }
-	set_by_lua_block $skynet_server_domain { return "{{SERVER_DOMAIN}}" == "" and "{{PORTAL_DOMAIN}}" or "{{SERVER_DOMAIN}}" }
+	set_by_lua_block $skynet_server_domain {
+		-- fall back to portal domain if server domain is not defined
+		if "{{SERVER_DOMAIN}}" == "" then
+			return "{{PORTAL_DOMAIN}}"
+		end
+		return "{{SERVER_DOMAIN}}"
+	}
 
 	ssl_certificate     /data/caddy/caddy/certificates/acme-v02.api.letsencrypt.org-directory/wildcard_.{{PORTAL_DOMAIN}}/wildcard_.{{PORTAL_DOMAIN}}.crt;
 	ssl_certificate_key	/data/caddy/caddy/certificates/acme-v02.api.letsencrypt.org-directory/wildcard_.{{PORTAL_DOMAIN}}/wildcard_.{{PORTAL_DOMAIN}}.key;