diff --git a/formatting.cabal b/formatting.cabal
--- a/formatting.cabal
+++ b/formatting.cabal
@@ -1,5 +1,5 @@
 name:                formatting
-version:             6.2.3
+version:             6.2.4
 synopsis:            Combinator-based type-safe formatting (like printf() or FORMAT)
 description:         Combinator-based type-safe formatting (like printf() or FORMAT), modelled from the HoleyMonoids package.
 license:             BSD3
diff --git a/src/Formatting.hs b/src/Formatting.hs
--- a/src/Formatting.hs
+++ b/src/Formatting.hs
@@ -25,6 +25,7 @@
   (%.),
   now,
   later,
+  mapf,
   -- * Top-level functions
   format,
   sformat,
@@ -39,4 +40,3 @@
 
 import Formatting.Formatters
 import Formatting.Internal
-
diff --git a/src/Formatting/Internal.hs b/src/Formatting/Internal.hs
--- a/src/Formatting/Internal.hs
+++ b/src/Formatting/Internal.hs
@@ -43,6 +43,10 @@
 newtype Format r a =
   Format {runFormat :: (Builder -> r) -> a}
 
+-- | Not particularly useful, but could be.
+instance Functor (Format r) where
+  fmap f (Format k) = Format (\br -> f (k br))
+
 -- | Useful instance for applying two formatters to the same input
 -- argument. For example: @format (year <> "/" % month) now@ will
 -- yield @"2015/01"@.
@@ -116,6 +120,10 @@
 -- | Monadic indexed bind for holey monoids.
 bind :: Format r a -> (Builder -> Format r' r) -> Format r' a
 m `bind` f = Format $ \k -> runFormat m (\a -> runFormat (f a) k)
+
+-- | Functorial map over a formatter's input. Example: @format (mapf (drop 1) string) \"hello\"@
+mapf :: (a -> b) -> Format r (b -> t) -> Format r (a -> t)
+mapf f m = Format (\k -> runFormat m k . f)
 
 -- | Format a value of type @a@ using a function of type @a ->
 -- 'Builder'@. For example, @later (f :: Int -> Builder)@ produces