diff --git a/src/Prologue.hs b/src/Prologue.hs
index 3b06c8a57..ba5eb64eb 100644
--- a/src/Prologue.hs
+++ b/src/Prologue.hs
@@ -2,6 +2,7 @@
 module Prologue
   ( module X
   , eitherA
+  , eitherM
   , foldMapA
   , maybeM
   , maybeLast
@@ -79,6 +80,9 @@ fromMaybeLast b = fromMaybe b . getLast . foldMap (Last . Just)
 maybeM :: Applicative f => f a -> Maybe a -> f a
 maybeM f = maybe f pure
 
+eitherM :: Applicative f => (a -> f b) -> Either a b -> f b
+eitherM f = either f pure
+
 -- Promote a function to either-applicatives.
 eitherA :: Applicative f => (b -> f (Either a c)) -> Either a b -> f (Either a c)
 eitherA = either (pure . Left)