diff --git a/src/Pretty/Serialize.hs b/src/Pretty/Serialize.hs
index 3ef4206..5a7a767 100644
--- a/src/Pretty/Serialize.hs
+++ b/src/Pretty/Serialize.hs
@@ -57,10 +57,10 @@ type ContinuationSerializer a = (SerializerState -> (SerializerState, a))
 type Prepends = [StrictText] -> [StrictText]
 
 data SerializerState = SerializerState
-  { builder             :: Prepends
-  , indentation         :: !Indentation
+  { builder             :: Prepends -- this laziness is important
+  , indentation         :: {-# UNPACK #-} !Indentation
   , increaseIndentation :: !(Indentation -> Indentation)
-  , currentFieldIndex   :: !(Maybe Word)
+  , currentFieldIndex   :: {-# UNPACK #-} !(Maybe Word)
   }
 
 instance Applicative Serializer where