diff --git a/src/Data/Bifunctor/Join.hs b/src/Data/Bifunctor/Join.hs
index 6628c948b..c5d5b94ac 100644
--- a/src/Data/Bifunctor/Join.hs
+++ b/src/Data/Bifunctor/Join.hs
@@ -1,3 +1,6 @@
 module Data.Bifunctor.Join where
 
 newtype Join p a = { runJoin :: p a a }
+
+instance Bifunctor p => Functor (Join p) where
+  fmap f = Join . bimap f f . runJoin