diff --git a/machine.go b/machine.go
index 5b8a3ae..0193e8e 100644
--- a/machine.go
+++ b/machine.go
@@ -51,7 +51,7 @@ type Machine struct {
 	//
 	// GivenName is the name used in all DNS related
 	// parts of headscale.
-	GivenName   string
+	GivenName   string `gorm:"type:varchar(63);unique_index"`
 	NamespaceID uint
 	Namespace   Namespace `gorm:"foreignKey:NamespaceID"`