diff --git a/spritesheet.lua b/spritesheet.lua
index 88f3dd3..df00509 100644
--- a/spritesheet.lua
+++ b/spritesheet.lua
@@ -1,5 +1,5 @@
 
---local error = require 'errors' 'SpriteSheet2'
+local error = require 'errors' 'SpriteSheet2'
 
 --------------------------------------------------------------------------------
 -- Util
@@ -76,6 +76,8 @@ function Animation.new (self)
     assert(#self > 0)
     assert(type(self.time) == 'number' or #self == #self.time)
 
+    assert(self.wrap == nil or self.wrap == true or self.wrap == false)
+
     local  self = setmetatable(self, Animation)
            self.duration      =  calculate_animation_duration(self)
            self.is_animation  =  true