--- a/Graphics/EasyRender/Internal.hs
+++ b/Graphics/EasyRender/Internal.hs
@@ -36,6 +36,7 @@
 
 import Codec.Compression.Zlib
 import Control.Monad.State
+import Control.Monad (when)
 import qualified Data.ByteString.Lazy as ByteString
 import Data.Char
 import Data.List