diff --git a/firewall/config.go b/firewall/config.go
index cd7a4d2a..d4659972 100644
--- a/firewall/config.go
+++ b/firewall/config.go
@@ -76,6 +76,7 @@ func registerConfig() error {
 			config.UnitAnnotation:         "seconds",
 			config.CategoryAnnotation:     "General",
 		},
+		ValidationRegex: `^[1-9][0-9]{1,5}$`,
 	})
 	if err != nil {
 		return err
diff --git a/resolver/config.go b/resolver/config.go
index 2a360d82..061b6bc3 100644
--- a/resolver/config.go
+++ b/resolver/config.go
@@ -166,6 +166,7 @@ The format is: "protocol://ip:port?parameter=value&parameter=value"
 			config.UnitAnnotation:         "seconds",
 			config.CategoryAnnotation:     "Servers",
 		},
+		ValidationRegex: `^[1-9][0-9]{1,5}$`,
 	})
 	if err != nil {
 		return err