diff --git a/src/main/scala/li/cil/oc/server/component/UpgradeLeash.scala b/src/main/scala/li/cil/oc/server/component/UpgradeLeash.scala
index 0476482da..6255843b9 100644
--- a/src/main/scala/li/cil/oc/server/component/UpgradeLeash.scala
+++ b/src/main/scala/li/cil/oc/server/component/UpgradeLeash.scala
@@ -51,7 +51,7 @@ class UpgradeLeash(val host: Entity with li.cil.oc.api.internal.Drone) extends A
 
   override def position = BlockPosition(host.asInstanceOf[Entity])
 
-  @Callback(doc = """function(side:number):boolean -- Tries to put an entity on the specified side of the device onto a leash.""")
+  @Callback(doc = """function(side:number):boolean, string -- Tries to put an entity on the specified side of the device onto a leash.""")
   def leash(context: Context, args: Arguments): Array[AnyRef] = {
     if (leashedEntities.size >= MaxLeashedEntities) return result(Unit, "too many leashed entities")
     val side = args.checkSideAny(0)
@@ -67,7 +67,7 @@ class UpgradeLeash(val host: Entity with li.cil.oc.api.internal.Drone) extends A
           result(true)
         }
         else {
-          result(false, "don't has leash to be shrink")
+          result(false, "don't have leash to be shrink")
         }
       case _ => result(false, "no unleashed entity")
     }