diff --git a/src/Pretty/Serialize.hs b/src/Pretty/Serialize.hs
index 6ec5f5c..95e1c16 100644
--- a/src/Pretty/Serialize.hs
+++ b/src/Pretty/Serialize.hs
@@ -52,10 +52,10 @@ newtype Serializer a = Serializer (SerializerState -> (SerializerState, a))
   deriving stock (Functor)
 
 data SerializerState = SerializerState
-  { builder             :: Builder
-  , indentation         :: Indentation
-  , increaseIndentation :: Indentation -> Indentation
-  , currentFieldIndex   :: Maybe Word
+  { builder             :: !Builder
+  , indentation         :: !Indentation
+  , increaseIndentation :: !(Indentation -> Indentation)
+  , currentFieldIndex   :: !(Maybe Word)
   }
 
 instance Applicative Serializer where